=head1 NAME perlguts - Perl's Internal Functions =head1 DESCRIPTION This document attempts to describe some of the internal functions of the Perl executable. It is far from complete and probably contains many errors. Please refer any questions or comments to the author below. =head1 Variables =head2 Datatypes Perl has three typedefs that handle Perl's three main data types: SV Scalar Value AV Array Value HV Hash Value Each typedef has specific routines that manipulate the various data types. =head2 What is an "IV"? Perl uses a special typedef IV which is a simple integer type that is guaranteed to be large enough to hold a pointer (as well as an integer). Perl also uses two special typedefs, I32 and I16, which will always be at least 32-bits and 16-bits long, respectively. =head2 Working with SVs An SV can be created and loaded with one command. There are four types of values that can be loaded: an integer value (IV), a double (NV), a string, (PV), and another scalar (SV). The six routines are: SV* newSViv(IV); SV* newSVnv(double); SV* newSVpv(char*, int); SV* newSVpvn(char*, int); SV* newSVpvf(const char*, ...); SV* newSVsv(SV*); To change the value of an *already-existing* SV, there are seven routines: void sv_setiv(SV*, IV); void sv_setuv(SV*, UV); void sv_setnv(SV*, double); void sv_setpv(SV*, char*); void sv_setpvn(SV*, char*, int) void sv_setpvf(SV*, const char*, ...); void sv_setpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool); void sv_setsv(SV*, SV*); Notice that you can choose to specify the length of the string to be assigned by using C, C, or C, or you may allow Perl to calculate the length by using C or by specifying 0 as the second argument to C. Be warned, though, that Perl will determine the string's length by using C, which depends on the string terminating with a NUL character. The arguments of C are processed like C, and the formatted output becomes the value. C is an analogue of C, but it allows you to specify either a pointer to a variable argument list or the address and length of an array of SVs. The last argument points to a boolean; on return, if that boolean is true, then locale-specific information has been used to format the string, and the string's contents are therefore untrustworty (see L). This pointer may be NULL if that information is not important. Note that this function requires you to specify the length of the format. The C functions are not generic enough to operate on values that have "magic". See L later in this document. All SVs that contain strings should be terminated with a NUL character. If it is not NUL-terminated there is a risk of core dumps and corruptions from code which passes the string to C functions or system calls which expect a NUL-terminated string. Perl's own functions typically add a trailing NUL for this reason. Nevertheless, you should be very careful when you pass a string stored in an SV to a C function or system call. To access the actual value that an SV points to, you can use the macros: SvIV(SV*) SvNV(SV*) SvPV(SV*, STRLEN len) which will automatically coerce the actual scalar type into an IV, double, or string. In the C macro, the length of the string returned is placed into the variable C (this is a macro, so you do I use C<&len>). If you do not care what the length of the data is, use the global variable C. Remember, however, that Perl allows arbitrary strings of data that may both contain NULs and might not be terminated by a NUL. If you want to know if the scalar value is TRUE, you can use: SvTRUE(SV*) Although Perl will automatically grow strings for you, if you need to force Perl to allocate more memory for your SV, you can use the macro SvGROW(SV*, STRLEN newlen) which will determine if more memory needs to be allocated. If so, it will call the function C. Note that C can only increase, not decrease, the allocated memory of an SV and that it does not automatically add a byte for the a trailing NUL (perl's own string functions typically do C). If you have an SV and want to know what kind of data Perl thinks is stored in it, you can use the following macros to check the type of SV you have. SvIOK(SV*) SvNOK(SV*) SvPOK(SV*) You can get and set the current length of the string stored in an SV with the following macros: SvCUR(SV*) SvCUR_set(SV*, I32 val) You can also get a pointer to the end of the string stored in the SV with the macro: SvEND(SV*) But note that these last three macros are valid only if C is true. If you want to append something to the end of string stored in an C, you can use the following functions: void sv_catpv(SV*, char*); void sv_catpvn(SV*, char*, int); void sv_catpvf(SV*, const char*, ...); void sv_catpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool); void sv_catsv(SV*, SV*); The first function calculates the length of the string to be appended by using C. In the second, you specify the length of the string yourself. The third function processes its arguments like C and appends the formatted output. The fourth function works like C. You can specify the address and length of an array of SVs instead of the va_list argument. The fifth function extends the string stored in the first SV with the string stored in the second SV. It also forces the second SV to be interpreted as a string. The C functions are not generic enough to operate on values that have "magic". See L later in this document. If you know the name of a scalar variable, you can get a pointer to its SV by using the following: SV* perl_get_sv("package::varname", FALSE); This returns NULL if the variable does not exist. If you want to know if this variable (or any other SV) is actually C, you can call: SvOK(SV*) The scalar C value is stored in an SV instance called C. Its address can be used whenever an C is needed. There are also the two values C and C, which contain Boolean TRUE and FALSE values, respectively. Like C, their addresses can be used whenever an C is needed. Do not be fooled into thinking that C<(SV *) 0> is the same as C<&PL_sv_undef>. Take this code: SV* sv = (SV*) 0; if (I-am-to-return-a-real-value) { sv = sv_2mortal(newSViv(42)); } sv_setsv(ST(0), sv); This code tries to return a new SV (which contains the value 42) if it should return a real value, or undef otherwise. Instead it has returned a NULL pointer which, somewhere down the line, will cause a segmentation violation, bus error, or just weird results. Change the zero to C<&PL_sv_undef> in the first line and all will be well. To free an SV that you've created, call C. Normally this call is not necessary (see L). =head2 What's Really Stored in an SV? Recall that the usual method of determining the type of scalar you have is to use C macros. Because a scalar can be both a number and a string, usually these macros will always return TRUE and calling the C macros will do the appropriate conversion of string to integer/double or integer/double to string. If you I need to know if you have an integer, double, or string pointer in an SV, you can use the following three macros instead: SvIOKp(SV*) SvNOKp(SV*) SvPOKp(SV*) These will tell you if you truly have an integer, double, or string pointer stored in your SV. The "p" stands for private. In general, though, it's best to use the C macros. =head2 Working with AVs There are two ways to create and load an AV. The first method creates an empty AV: AV* newAV(); The second method both creates the AV and initially populates it with SVs: AV* av_make(I32 num, SV **ptr); The second argument points to an array containing C C's. Once the AV has been created, the SVs can be destroyed, if so desired. Once the AV has been created, the following operations are possible on AVs: void av_push(AV*, SV*); SV* av_pop(AV*); SV* av_shift(AV*); void av_unshift(AV*, I32 num); These should be familiar operations, with the exception of C. This routine adds C elements at the front of the array with the C value. You must then use C (described below) to assign values to these new elements. Here are some other functions: I32 av_len(AV*); SV** av_fetch(AV*, I32 key, I32 lval); SV** av_store(AV*, I32 key, SV* val); The C function returns the highest index value in array (just like $#array in Perl). If the array is empty, -1 is returned. The C function returns the value at index C, but if C is non-zero, then C will store an undef value at that index. The C function stores the value C at index C, and does not increment the reference count of C. Thus the caller is responsible for taking care of that, and if C returns NULL, the caller will have to decrement the reference count to avoid a memory leak. Note that C and C both return C's, not C's as their return value. void av_clear(AV*); void av_undef(AV*); void av_extend(AV*, I32 key); The C function deletes all the elements in the AV* array, but does not actually delete the array itself. The C function will delete all the elements in the array plus the array itself. The C function extends the array so that it contains C elements. If C is less than the current length of the array, then nothing is done. If you know the name of an array variable, you can get a pointer to its AV by using the following: AV* perl_get_av("package::varname", FALSE); This returns NULL if the variable does not exist. See L for more information on how to use the array access functions on tied arrays. =head2 Working with HVs To create an HV, you use the following routine: HV* newHV(); Once the HV has been created, the following operations are possible on HVs: SV** hv_store(HV*, char* key, U32 klen, SV* val, U32 hash); SV** hv_fetch(HV*, char* key, U32 klen, I32 lval); The C parameter is the length of the key being passed in (Note that you cannot pass 0 in as a value of C to tell Perl to measure the length of the key). The C argument contains the SV pointer to the scalar being stored, and C is the precomputed hash value (zero if you want C to calculate it for you). The C parameter indicates whether this fetch is actually a part of a store operation, in which case a new undefined value will be added to the HV with the supplied key and C will return as if the value had already existed. Remember that C and C return C's and not just C. To access the scalar value, you must first dereference the return value. However, you should check to make sure that the return value is not NULL before dereferencing it. These two functions check if a hash table entry exists, and deletes it. bool hv_exists(HV*, char* key, U32 klen); SV* hv_delete(HV*, char* key, U32 klen, I32 flags); If C does not include the C flag then C will create and return a mortal copy of the deleted value. And more miscellaneous functions: void hv_clear(HV*); void hv_undef(HV*); Like their AV counterparts, C deletes all the entries in the hash table but does not actually delete the hash table. The C deletes both the entries and the hash table itself. Perl keeps the actual data in linked list of structures with a typedef of HE. These contain the actual key and value pointers (plus extra administrative overhead). The key is a string pointer; the value is an C. However, once you have an C, to get the actual key and value, use the routines specified below. I32 hv_iterinit(HV*); /* Prepares starting point to traverse hash table */ HE* hv_iternext(HV*); /* Get the next entry, and return a pointer to a structure that has both the key and value */ char* hv_iterkey(HE* entry, I32* retlen); /* Get the key from an HE structure and also return the length of the key string */ SV* hv_iterval(HV*, HE* entry); /* Return a SV pointer to the value of the HE structure */ SV* hv_iternextsv(HV*, char** key, I32* retlen); /* This convenience routine combines hv_iternext, hv_iterkey, and hv_iterval. The key and retlen arguments are return values for the key and its length. The value is returned in the SV* argument */ If you know the name of a hash variable, you can get a pointer to its HV by using the following: HV* perl_get_hv("package::varname", FALSE); This returns NULL if the variable does not exist. The hash algorithm is defined in the C macro: i = klen; hash = 0; s = key; while (i--) hash = hash * 33 + *s++; See L for more information on how to use the hash access functions on tied hashes. =head2 Hash API Extensions Beginning with version 5.004, the following functions are also supported: HE* hv_fetch_ent (HV* tb, SV* key, I32 lval, U32 hash); HE* hv_store_ent (HV* tb, SV* key, SV* val, U32 hash); bool hv_exists_ent (HV* tb, SV* key, U32 hash); SV* hv_delete_ent (HV* tb, SV* key, I32 flags, U32 hash); SV* hv_iterkeysv (HE* entry); Note that these functions take C keys, which simplifies writing of extension code that deals with hash structures. These functions also allow passing of C keys to C functions without forcing you to stringify the keys (unlike the previous set of functions). They also return and accept whole hash entries (C), making their use more efficient (since the hash number for a particular string doesn't have to be recomputed every time). See L later in this document for detailed descriptions. The following macros must always be used to access the contents of hash entries. Note that the arguments to these macros must be simple variables, since they may get evaluated more than once. See L later in this document for detailed descriptions of these macros. HePV(HE* he, STRLEN len) HeVAL(HE* he) HeHASH(HE* he) HeSVKEY(HE* he) HeSVKEY_force(HE* he) HeSVKEY_set(HE* he, SV* sv) These two lower level macros are defined, but must only be used when dealing with keys that are not Cs: HeKEY(HE* he) HeKLEN(HE* he) Note that both C and C do not increment the reference count of the stored C, which is the caller's responsibility. If these functions return a NULL value, the caller will usually have to decrement the reference count of C to avoid a memory leak. =head2 References References are a special type of scalar that point to other data types (including references). To create a reference, use either of the following functions: SV* newRV_inc((SV*) thing); SV* newRV_noinc((SV*) thing); The C argument can be any of an C, C, or C. The functions are identical except that C increments the reference count of the C, while C does not. For historical reasons, C is a synonym for C. Once you have a reference, you can use the following macro to dereference the reference: SvRV(SV*) then call the appropriate routines, casting the returned C to either an C or C, if required. To determine if an SV is a reference, you can use the following macro: SvROK(SV*) To discover what type of value the reference refers to, use the following macro and then check the return value. SvTYPE(SvRV(SV*)) The most useful types that will be returned are: SVt_IV Scalar SVt_NV Scalar SVt_PV Scalar SVt_RV Scalar SVt_PVAV Array SVt_PVHV Hash SVt_PVCV Code SVt_PVGV Glob (possible a file handle) SVt_PVMG Blessed or Magical Scalar See the sv.h header file for more details. =head2 Blessed References and Class Objects References are also used to support object-oriented programming. In the OO lexicon, an object is simply a reference that has been blessed into a package (or class). Once blessed, the programmer may now use the reference to access the various methods in the class. A reference can be blessed into a package with the following function: SV* sv_bless(SV* sv, HV* stash); The C argument must be a reference. The C argument specifies which class the reference will belong to. See L for information on converting class names into stashes. /* Still under construction */ Upgrades rv to reference if not already one. Creates new SV for rv to point to. If C is non-null, the SV is blessed into the specified class. SV is returned. SV* newSVrv(SV* rv, char* classname); Copies integer or double into an SV whose reference is C. SV is blessed if C is non-null. SV* sv_setref_iv(SV* rv, char* classname, IV iv); SV* sv_setref_nv(SV* rv, char* classname, NV iv); Copies the pointer value (I) into an SV whose reference is rv. SV is blessed if C is non-null. SV* sv_setref_pv(SV* rv, char* classname, PV iv); Copies string into an SV whose reference is C. Set length to 0 to let Perl calculate the string length. SV is blessed if C is non-null. SV* sv_setref_pvn(SV* rv, char* classname, PV iv, int length); Tests whether the SV is blessed into the specified class. It does not check inheritance relationships. int sv_isa(SV* sv, char* name); Tests whether the SV is a reference to a blessed object. int sv_isobject(SV* sv); Tests whether the SV is derived from the specified class. SV can be either a reference to a blessed object or a string containing a class name. This is the function implementing the C functionality. bool sv_derived_from(SV* sv, char* name); To check if you've got an object derived from a specific class you have to write: if (sv_isobject(sv) && sv_derived_from(sv, class)) { ... } =head2 Creating New Variables To create a new Perl variable with an undef value which can be accessed from your Perl script, use the following routines, depending on the variable type. SV* perl_get_sv("package::varname", TRUE); AV* perl_get_av("package::varname", TRUE); HV* perl_get_hv("package::varname", TRUE); Notice the use of TRUE as the second parameter. The new variable can now be set, using the routines appropriate to the data type. There are additional macros whose values may be bitwise OR'ed with the C argument to enable certain extra features. Those bits are: GV_ADDMULTI Marks the variable as multiply defined, thus preventing the "Name used only once: possible typo" warning. GV_ADDWARN Issues the warning "Had to create unexpectedly" if the variable did not exist before the function was called. If you do not specify a package name, the variable is created in the current package. =head2 Reference Counts and Mortality Perl uses an reference count-driven garbage collection mechanism. SVs, AVs, or HVs (xV for short in the following) start their life with a reference count of 1. If the reference count of an xV ever drops to 0, then it will be destroyed and its memory made available for reuse. This normally doesn't happen at the Perl level unless a variable is undef'ed or the last variable holding a reference to it is changed or overwritten. At the internal level, however, reference counts can be manipulated with the following macros: int SvREFCNT(SV* sv); SV* SvREFCNT_inc(SV* sv); void SvREFCNT_dec(SV* sv); However, there is one other function which manipulates the reference count of its argument. The C function, you will recall, creates a reference to the specified argument. As a side effect, it increments the argument's reference count. If this is not what you want, use C instead. For example, imagine you want to return a reference from an XSUB function. Inside the XSUB routine, you create an SV which initially has a reference count of one. Then you call C, passing it the just-created SV. This returns the reference as a new SV, but the reference count of the SV you passed to C has been incremented to two. Now you return the reference from the XSUB routine and forget about the SV. But Perl hasn't! Whenever the returned reference is destroyed, the reference count of the original SV is decreased to one and nothing happens. The SV will hang around without any way to access it until Perl itself terminates. This is a memory leak. The correct procedure, then, is to use C instead of C. Then, if and when the last reference is destroyed, the reference count of the SV will go to zero and it will be destroyed, stopping any memory leak. There are some convenience functions available that can help with the destruction of xVs. These functions introduce the concept of "mortality". An xV that is mortal has had its reference count marked to be decremented, but not actually decremented, until "a short time later". Generally the term "short time later" means a single Perl statement, such as a call to an XSUB function. The actual determinant for when mortal xVs have their reference count decremented depends on two macros, SAVETMPS and FREETMPS. See L and L for more details on these macros. "Mortalization" then is at its simplest a deferred C. However, if you mortalize a variable twice, the reference count will later be decremented twice. You should be careful about creating mortal variables. Strange things can happen if you make the same value mortal within multiple contexts, or if you make a variable mortal multiple times. To create a mortal variable, use the functions: SV* sv_newmortal() SV* sv_2mortal(SV*) SV* sv_mortalcopy(SV*) The first call creates a mortal SV, the second converts an existing SV to a mortal SV (and thus defers a call to C), and the third creates a mortal copy of an existing SV. The mortal routines are not just for SVs -- AVs and HVs can be made mortal by passing their address (type-casted to C) to the C or C routines. =head2 Stashes and Globs A "stash" is a hash that contains all of the different objects that are contained within a package. Each key of the stash is a symbol name (shared by all the different types of objects that have the same name), and each value in the hash table is a GV (Glob Value). This GV in turn contains references to the various objects of that name, including (but not limited to) the following: Scalar Value Array Value Hash Value I/O Handle Format Subroutine There is a single stash called "PL_defstash" that holds the items that exist in the "main" package. To get at the items in other packages, append the string "::" to the package name. The items in the "Foo" package are in the stash "Foo::" in PL_defstash. The items in the "Bar::Baz" package are in the stash "Baz::" in "Bar::"'s stash. To get the stash pointer for a particular package, use the function: HV* gv_stashpv(char* name, I32 create) HV* gv_stashsv(SV*, I32 create) The first function takes a literal string, the second uses the string stored in the SV. Remember that a stash is just a hash table, so you get back an C. The C flag will create a new package if it is set. The name that C wants is the name of the package whose symbol table you want. The default package is called C
. If you have multiply nested packages, pass their names to C, separated by C<::> as in the Perl language itself. Alternately, if you have an SV that is a blessed reference, you can find out the stash pointer by using: HV* SvSTASH(SvRV(SV*)); then use the following to get the package name itself: char* HvNAME(HV* stash); If you need to bless or re-bless an object you can use the following function: SV* sv_bless(SV*, HV* stash) where the first argument, an C, must be a reference, and the second argument is a stash. The returned C can now be used in the same way as any other SV. For more information on references and blessings, consult L. =head2 Double-Typed SVs Scalar variables normally contain only one type of value, an integer, double, pointer, or reference. Perl will automatically convert the actual scalar data from the stored type into the requested type. Some scalar variables contain more than one type of scalar data. For example, the variable C<$!> contains either the numeric value of C or its string equivalent from either C or C. To force multiple data values into an SV, you must do two things: use the C routines to add the additional scalar type, then set a flag so that Perl will believe it contains more than one type of data. The four macros to set the flags are: SvIOK_on SvNOK_on SvPOK_on SvROK_on The particular macro you must use depends on which C routine you called first. This is because every C routine turns on only the bit for the particular type of data being set, and turns off all the rest. For example, to create a new Perl variable called "dberror" that contains both the numeric and descriptive string error values, you could use the following code: extern int dberror; extern char *dberror_list; SV* sv = perl_get_sv("dberror", TRUE); sv_setiv(sv, (IV) dberror); sv_setpv(sv, dberror_list[dberror]); SvIOK_on(sv); If the order of C and C had been reversed, then the macro C would need to be called instead of C. =head2 Magic Variables [This section still under construction. Ignore everything here. Post no bills. Everything not permitted is forbidden.] Any SV may be magical, that is, it has special features that a normal SV does not have. These features are stored in the SV structure in a linked list of C's, typedef'ed to C. struct magic { MAGIC* mg_moremagic; MGVTBL* mg_virtual; U16 mg_private; char mg_type; U8 mg_flags; SV* mg_obj; char* mg_ptr; I32 mg_len; }; Note this is current as of patchlevel 0, and could change at any time. =head2 Assigning Magic Perl adds magic to an SV using the sv_magic function: void sv_magic(SV* sv, SV* obj, int how, char* name, I32 namlen); The C argument is a pointer to the SV that is to acquire a new magical feature. If C is not already magical, Perl uses the C macro to set the C flag for the C. Perl then continues by adding it to the beginning of the linked list of magical features. Any prior entry of the same type of magic is deleted. Note that this can be overridden, and multiple instances of the same type of magic can be associated with an SV. The C and C arguments are used to associate a string with the magic, typically the name of a variable. C is stored in the C field and if C is non-null and C >= 0 a malloc'd copy of the name is stored in C field. The sv_magic function uses C to determine which, if any, predefined "Magic Virtual Table" should be assigned to the C field. See the "Magic Virtual Table" section below. The C argument is also stored in the C field. The C argument is stored in the C field of the C structure. If it is not the same as the C argument, the reference count of the C object is incremented. If it is the same, or if the C argument is "#", or if it is a NULL pointer, then C is merely stored, without the reference count being incremented. There is also a function to add magic to an C: void hv_magic(HV *hv, GV *gv, int how); This simply calls C and coerces the C argument into an C. To remove the magic from an SV, call the function sv_unmagic: void sv_unmagic(SV *sv, int type); The C argument should be equal to the C value when the C was initially made magical. =head2 Magic Virtual Tables The C field in the C structure is a pointer to a C, which is a structure of function pointers and stands for "Magic Virtual Table" to handle the various operations that might be applied to that variable. The C has five pointers to the following routine types: int (*svt_get)(SV* sv, MAGIC* mg); int (*svt_set)(SV* sv, MAGIC* mg); U32 (*svt_len)(SV* sv, MAGIC* mg); int (*svt_clear)(SV* sv, MAGIC* mg); int (*svt_free)(SV* sv, MAGIC* mg); This MGVTBL structure is set at compile-time in C and there are currently 19 types (or 21 with overloading turned on). These different structures contain pointers to various routines that perform additional actions depending on which function is being called. Function pointer Action taken ---------------- ------------ svt_get Do something after the value of the SV is retrieved. svt_set Do something after the SV is assigned a value. svt_len Report on the SV's length. svt_clear Clear something the SV represents. svt_free Free any extra storage associated with the SV. For instance, the MGVTBL structure called C (which corresponds to an C of '\0') contains: { magic_get, magic_set, magic_len, 0, 0 } Thus, when an SV is determined to be magical and of type '\0', if a get operation is being performed, the routine C is called. All the various routines for the various magical types begin with C. The current kinds of Magic Virtual Tables are: mg_type MGVTBL Type of magic ------- ------ ---------------------------- \0 vtbl_sv Special scalar variable A vtbl_amagic %OVERLOAD hash a vtbl_amagicelem %OVERLOAD hash element c (none) Holds overload table (AMT) on stash B vtbl_bm Boyer-Moore (fast string search) E vtbl_env %ENV hash e vtbl_envelem %ENV hash element f vtbl_fm Formline ('compiled' format) g vtbl_mglob m//g target / study()ed string I vtbl_isa @ISA array i vtbl_isaelem @ISA array element k vtbl_nkeys scalar(keys()) lvalue L (none) Debugger %_'s C field points to a C structure: struct ufuncs { I32 (*uf_val)(IV, SV*); I32 (*uf_set)(IV, SV*); IV uf_index; }; When the SV is read from or written to, the C or C function will be called with C as the first arg and a pointer to the SV as the second. Note that because multiple extensions may be using '~' or 'U' magic, it is important for extensions to take extra care to avoid conflict. Typically only using the magic on objects blessed into the same class as the extension is sufficient. For '~' magic, it may also be appropriate to add an I32 'signature' at the top of the private data area and check that. Also note that the C and C functions described earlier do B invoke 'set' magic on their targets. This must be done by the user either by calling the C macro after calling these functions, or by using one of the C or C functions. Similarly, generic C code must call the C macro to invoke any 'get' magic if they use an SV obtained from external sources in functions that don't handle magic. L later in this document identifies such functions. For example, calls to the C functions typically need to be followed by C, but they don't need a prior C since their implementation handles 'get' magic. =head2 Finding Magic MAGIC* mg_find(SV*, int type); /* Finds the magic pointer of that type */ This routine returns a pointer to the C structure stored in the SV. If the SV does not have that magical feature, C is returned. Also, if the SV is not of type SVt_PVMG, Perl may core dump. int mg_copy(SV* sv, SV* nsv, char* key, STRLEN klen); This routine checks to see what types of magic C has. If the mg_type field is an uppercase letter, then the mg_obj is copied to C, but the mg_type field is changed to be the lowercase letter. =head2 Understanding the Magic of Tied Hashes and Arrays Tied hashes and arrays are magical beasts of the 'P' magic type. WARNING: As of the 5.004 release, proper usage of the array and hash access functions requires understanding a few caveats. Some of these caveats are actually considered bugs in the API, to be fixed in later releases, and are bracketed with [MAYCHANGE] below. If you find yourself actually applying such information in this section, be aware that the behavior may change in the future, umm, without warning. The C function, when given a tied array argument, merely copies the magic of the array onto the value to be "stored", using C. It may also return NULL, indicating that the value did not actually need to be stored in the array. [MAYCHANGE] After a call to C on a tied array, the caller will usually need to call C to actually invoke the perl level "STORE" method on the TIEARRAY object. If C did return NULL, a call to C will also be usually necessary to avoid a memory leak. [/MAYCHANGE] The previous paragraph is applicable verbatim to tied hash access using the C and C functions as well. C and the corresponding hash functions C and C actually return an undefined mortal value whose magic has been initialized using C. Note the value so returned does not need to be deallocated, as it is already mortal. [MAYCHANGE] But you will need to call C on the returned value in order to actually invoke the perl level "FETCH" method on the underlying TIE object. Similarly, you may also call C on the return value after possibly assigning a suitable value to it using C, which will invoke the "STORE" method on the TIE object. [/MAYCHANGE] [MAYCHANGE] In other words, the array or hash fetch/store functions don't really fetch and store actual values in the case of tied arrays and hashes. They merely call C to attach magic to the values that were meant to be "stored" or "fetched". Later calls to C and C actually do the job of invoking the TIE methods on the underlying objects. Thus the magic mechanism currently implements a kind of lazy access to arrays and hashes. Currently (as of perl version 5.004), use of the hash and array access functions requires the user to be aware of whether they are operating on "normal" hashes and arrays, or on their tied variants. The API may be changed to provide more transparent access to both tied and normal data types in future versions. [/MAYCHANGE] You would do well to understand that the TIEARRAY and TIEHASH interfaces are mere sugar to invoke some perl method calls while using the uniform hash and array syntax. The use of this sugar imposes some overhead (typically about two to four extra opcodes per FETCH/STORE operation, in addition to the creation of all the mortal variables required to invoke the methods). This overhead will be comparatively small if the TIE methods are themselves substantial, but if they are only a few statements long, the overhead will not be insignificant. =head2 Localizing changes Perl has a very handy construction { local $var = 2; ... } This construction is I equivalent to { my $oldvar = $var; $var = 2; ... $var = $oldvar; } The biggest difference is that the first construction would reinstate the initial value of $var, irrespective of how control exits the block: C, C, C/C etc. It is a little bit more efficient as well. There is a way to achieve a similar task from C via Perl API: create a I, and arrange for some changes to be automatically undone at the end of it, either explicit, or via a non-local exit (via die()). A I-like construct is created by a pair of C/C macros (see L). Such a construct may be created specially for some important localized task, or an existing one (like boundaries of enclosing Perl subroutine/block, or an existing pair for freeing TMPs) may be used. (In the second case the overhead of additional localization must be almost negligible.) Note that any XSUB is automatically enclosed in an C/C pair. Inside such a I the following service is available: =over =item C =item C =item C =item C These macros arrange things to restore the value of integer variable C at the end of enclosing I. =item C =item C These macros arrange things to restore the value of pointers C and C

. C must be a pointer of a type which survives conversion to C and back, C

should be able to survive conversion to C and back. =item C The refcount of C would be decremented at the end of I. This is similar to C, which should (?) be used instead. =item C The C is op_free()ed at the end of I. =item C The chunk of memory which is pointed to by C

is Safefree()ed at the end of I. =item C Clears a slot in the current scratchpad which corresponds to C at the end of I. =item C The key C of C is deleted at the end of I. The string pointed to by C is Safefree()ed. If one has a I in short-lived storage, the corresponding string may be reallocated like this: SAVEDELETE(PL_defstash, savepv(tmpbuf), strlen(tmpbuf)); =item C At the end of I the function C is called with the only argument (of type C) C

. =item C The current offset on the Perl internal stack (cf. C) is restored at the end of I. =back The following API list contains functions, thus one needs to provide pointers to the modifiable data explicitly (either C pointers, or Perlish Cs). Where the above macros take C, a similar function takes C. =over =item C Equivalent to Perl code C. =item C =item C Similar to C, but localize C<@gv> and C<%gv>. =item C Duplicates the current value of C, on the exit from the current C/C I will restore the value of C using the stored value. =item C A variant of C which takes multiple arguments via an array C of C of length C. =item C Similar to C, but will reinstate a C. =item C =item C Similar to C, but localize C and C. =back The C module implements localization of the basic types within the I. People who are interested in how to localize things in the containing scope should take a look there too. =head1 Subroutines =head2 XSUBs and the Argument Stack The XSUB mechanism is a simple way for Perl programs to access C subroutines. An XSUB routine will have a stack that contains the arguments from the Perl program, and a way to map from the Perl data structures to a C equivalent. The stack arguments are accessible through the C macro, which returns the C'th stack argument. Argument 0 is the first argument passed in the Perl subroutine call. These arguments are C, and can be used anywhere an C is used. Most of the time, output from the C routine can be handled through use of the RETVAL and OUTPUT directives. However, there are some cases where the argument stack is not already long enough to handle all the return values. An example is the POSIX tzname() call, which takes no arguments, but returns two, the local time zone's standard and summer time abbreviations. To handle this situation, the PPCODE directive is used and the stack is extended using the macro: EXTEND(SP, num); where C is the macro that represents the local copy of the stack pointer, and C is the number of elements the stack should be extended by. Now that there is room on the stack, values can be pushed on it using the macros to push IVs, doubles, strings, and SV pointers respectively: PUSHi(IV) PUSHn(double) PUSHp(char*, I32) PUSHs(SV*) And now the Perl program calling C, the two values will be assigned as in: ($standard_abbrev, $summer_abbrev) = POSIX::tzname; An alternate (and possibly simpler) method to pushing values on the stack is to use the macros: XPUSHi(IV) XPUSHn(double) XPUSHp(char*, I32) XPUSHs(SV*) These macros automatically adjust the stack for you, if needed. Thus, you do not need to call C to extend the stack. For more information, consult L and L. =head2 Calling Perl Routines from within C Programs There are four routines that can be used to call a Perl subroutine from within a C program. These four are: I32 perl_call_sv(SV*, I32); I32 perl_call_pv(char*, I32); I32 perl_call_method(char*, I32); I32 perl_call_argv(char*, I32, register char**); The routine most often used is C. The C argument contains either the name of the Perl subroutine to be called, or a reference to the subroutine. The second argument consists of flags that control the context in which the subroutine is called, whether or not the subroutine is being passed arguments, how errors should be trapped, and how to treat return values. All four routines return the number of arguments that the subroutine returned on the Perl stack. When using any of these routines (except C), the programmer must manipulate the Perl stack. These include the following macros and functions: dSP SP PUSHMARK() PUTBACK SPAGAIN ENTER SAVETMPS FREETMPS LEAVE XPUSH*() POP*() For a detailed description of calling conventions from C to Perl, consult L. =head2 Memory Allocation It is suggested that you use the version of malloc that is distributed with Perl. It keeps pools of various sizes of unallocated memory in order to satisfy allocation requests more quickly. However, on some platforms, it may cause spurious malloc or free errors. New(x, pointer, number, type); Newc(x, pointer, number, type, cast); Newz(x, pointer, number, type); These three macros are used to initially allocate memory. The first argument C was a "magic cookie" that was used to keep track of who called the macro, to help when debugging memory problems. However, the current code makes no use of this feature (most Perl developers now use run-time memory checkers), so this argument can be any number. The second argument C should be the name of a variable that will point to the newly allocated memory. The third and fourth arguments C and C specify how many of the specified type of data structure should be allocated. The argument C is passed to C. The final argument to C, C, should be used if the C argument is different from the C argument. Unlike the C and C macros, the C macro calls C to zero out all the newly allocated memory. Renew(pointer, number, type); Renewc(pointer, number, type, cast); Safefree(pointer) These three macros are used to change a memory buffer size or to free a piece of memory no longer needed. The arguments to C and C match those of C and C with the exception of not needing the "magic cookie" argument. Move(source, dest, number, type); Copy(source, dest, number, type); Zero(dest, number, type); These three macros are used to move, copy, or zero out previously allocated memory. The C and C arguments point to the source and destination starting points. Perl will move, copy, or zero out C instances of the size of the C data structure (using the C function). =head2 PerlIO The most recent development releases of Perl has been experimenting with removing Perl's dependency on the "normal" standard I/O suite and allowing other stdio implementations to be used. This involves creating a new abstraction layer that then calls whichever implementation of stdio Perl was compiled with. All XSUBs should now use the functions in the PerlIO abstraction layer and not make any assumptions about what kind of stdio is being used. For a complete description of the PerlIO abstraction, consult L. =head2 Putting a C value on Perl stack A lot of opcodes (this is an elementary operation in the internal perl stack machine) put an SV* on the stack. However, as an optimization the corresponding SV is (usually) not recreated each time. The opcodes reuse specially assigned SVs (Is) which are (as a corollary) not constantly freed/created. Each of the targets is created only once (but see L below), and when an opcode needs to put an integer, a double, or a string on stack, it just sets the corresponding parts of its I and puts the I on stack. The macro to put this target on stack is C, and it is directly used in some opcodes, as well as indirectly in zillions of others, which use it via C<(X)PUSH[pni]>. =head2 Scratchpads The question remains on when the SVs which are Is for opcodes are created. The answer is that they are created when the current unit -- a subroutine or a file (for opcodes for statements outside of subroutines) -- is compiled. During this time a special anonymous Perl array is created, which is called a scratchpad for the current unit. A scratchpad keeps SVs which are lexicals for the current unit and are targets for opcodes. One can deduce that an SV lives on a scratchpad by looking on its flags: lexicals have C set, and Is have C set. The correspondence between OPs and Is is not 1-to-1. Different OPs in the compile tree of the unit can use the same target, if this would not conflict with the expected life of the temporary. =head2 Scratchpads and recursion In fact it is not 100% true that a compiled unit contains a pointer to the scratchpad AV. In fact it contains a pointer to an AV of (initially) one element, and this element is the scratchpad AV. Why do we need an extra level of indirection? The answer is B, and maybe (sometime soon) B. Both these can create several execution pointers going into the same subroutine. For the subroutine-child not write over the temporaries for the subroutine-parent (lifespan of which covers the call to the child), the parent and the child should have different scratchpads. (I the lexicals should be separate anyway!) So each subroutine is born with an array of scratchpads (of length 1). On each entry to the subroutine it is checked that the current depth of the recursion is not more than the length of this array, and if it is, new scratchpad is created and pushed into the array. The Is on this scratchpad are Cs, but they are already marked with correct flags. =head1 Compiled code =head2 Code tree Here we describe the internal form your code is converted to by Perl. Start with a simple example: $a = $b + $c; This is converted to a tree similar to this one: assign-to / \ + $a / \ $b $c (but slightly more complicated). This tree reflects the way Perl parsed your code, but has nothing to do with the execution order. There is an additional "thread" going through the nodes of the tree which shows the order of execution of the nodes. In our simplified example above it looks like: $b ---> $c ---> + ---> $a ---> assign-to But with the actual compile tree for C<$a = $b + $c> it is different: some nodes I. As a corollary, though the actual tree contains more nodes than our simplified example, the execution order is the same as in our example. =head2 Examining the tree If you have your perl compiled for debugging (usually done with C<-D optimize=-g> on C command line), you may examine the compiled tree by specifying C<-Dx> on the Perl command line. The output takes several lines per node, and for C<$b+$c> it looks like this: 5 TYPE = add ===> 6 TARG = 1 FLAGS = (SCALAR,KIDS) { TYPE = null ===> (4) (was rv2sv) FLAGS = (SCALAR,KIDS) { 3 TYPE = gvsv ===> 4 FLAGS = (SCALAR) GV = main::b } } { TYPE = null ===> (5) (was rv2sv) FLAGS = (SCALAR,KIDS) { 4 TYPE = gvsv ===> 5 FLAGS = (SCALAR) GV = main::c } } This tree has 5 nodes (one per C specifier), only 3 of them are not optimized away (one per number in the left column). The immediate children of the given node correspond to C<{}> pairs on the same level of indentation, thus this listing corresponds to the tree: add / \ null null | | gvsv gvsv The execution order is indicated by C<===E> marks, thus it is C<3 4 5 6> (node C<6> is not included into above listing), i.e., C. =head2 Compile pass 1: check routines The tree is created by the I while yacc code feeds it the constructions it recognizes. Since yacc works bottom-up, so does the first pass of perl compilation. What makes this pass interesting for perl developers is that some optimization may be performed on this pass. This is optimization by so-called I. The correspondence between node names and corresponding check routines is described in F (do not forget to run C if you modify this file). A check routine is called when the node is fully constructed except for the execution-order thread. Since at this time there are no back-links to the currently constructed node, one can do most any operation to the top-level node, including freeing it and/or creating new nodes above/below it. The check routine returns the node which should be inserted into the tree (if the top-level node was not modified, check routine returns its argument). By convention, check routines have names C. They are usually called from C subroutines (or C) (which in turn are called from F). =head2 Compile pass 1a: constant folding Immediately after the check routine is called the returned node is checked for being compile-time executable. If it is (the value is judged to be constant) it is immediately executed, and a I node with the "return value" of the corresponding subtree is substituted instead. The subtree is deleted. If constant folding was not performed, the execution-order thread is created. =head2 Compile pass 2: context propagation When a context for a part of compile tree is known, it is propagated down through the tree. At this time the context can have 5 values (instead of 2 for runtime context): void, boolean, scalar, list, and lvalue. In contrast with the pass 1 this pass is processed from top to bottom: a node's context determines the context for its children. Additional context-dependent optimizations are performed at this time. Since at this moment the compile tree contains back-references (via "thread" pointers), nodes cannot be free()d now. To allow optimized-away nodes at this stage, such nodes are null()ified instead of free()ing (i.e. their type is changed to OP_NULL). =head2 Compile pass 3: peephole optimization After the compile tree for a subroutine (or for an C or a file) is created, an additional pass over the code is performed. This pass is neither top-down or bottom-up, but in the execution order (with additional complications for conditionals). These optimizations are done in the subroutine peep(). Optimizations performed at this stage are subject to the same restrictions as in the pass 2. =head1 API LISTING This is a listing of functions, macros, flags, and variables that may be useful to extension writers or that may be found while reading other extensions. Note that all Perl API global variables must be referenced with the C prefix. Some macros are provided for compatibility with the older, unadorned names, but this support will be removed in a future release. It is strongly recommended that all Perl API functions that don't begin with C be referenced with an explicit C prefix. The sort order of the listing is case insensitive, with any occurrences of '_' ignored for the the purpose of sorting. =over 8 =item av_clear Clears an array, making it empty. Does not free the memory used by the array itself. void av_clear (AV* ar) =item av_extend Pre-extend an array. The C is the index to which the array should be extended. void av_extend (AV* ar, I32 key) =item av_fetch Returns the SV at the specified index in the array. The C is the index. If C is set then the fetch will be part of a store. Check that the return value is non-null before dereferencing it to a C. See L for more information on how to use this function on tied arrays. SV** av_fetch (AV* ar, I32 key, I32 lval) =item AvFILL Same as C. Deprecated, use C instead. =item av_len Returns the highest index in the array. Returns -1 if the array is empty. I32 av_len (AV* ar) =item av_make Creates a new AV and populates it with a list of SVs. The SVs are copied into the array, so they may be freed after the call to av_make. The new AV will have a reference count of 1. AV* av_make (I32 size, SV** svp) =item av_pop Pops an SV off the end of the array. Returns C<&PL_sv_undef> if the array is empty. SV* av_pop (AV* ar) =item av_push Pushes an SV onto the end of the array. The array will grow automatically to accommodate the addition. void av_push (AV* ar, SV* val) =item av_shift Shifts an SV off the beginning of the array. SV* av_shift (AV* ar) =item av_store Stores an SV in an array. The array index is specified as C. The return value will be NULL if the operation failed or if the value did not need to be actually stored within the array (as in the case of tied arrays). Otherwise it can be dereferenced to get the original C. Note that the caller is responsible for suitably incrementing the reference count of C before the call, and decrementing it if the function returned NULL. See L for more information on how to use this function on tied arrays. SV** av_store (AV* ar, I32 key, SV* val) =item av_undef Undefines the array. Frees the memory used by the array itself. void av_undef (AV* ar) =item av_unshift Unshift the given number of C values onto the beginning of the array. The array will grow automatically to accommodate the addition. You must then use C to assign values to these new elements. void av_unshift (AV* ar, I32 num) =item CLASS Variable which is setup by C to indicate the class name for a C++ XS constructor. This is always a C. See C and L. =item Copy The XSUB-writer's interface to the C C function. The C is the source, C is the destination, C is the number of items, and C is the type. May fail on overlapping copies. See also C. void Copy( s, d, n, t ) =item croak This is the XSUB-writer's interface to Perl's C function. Use this function the same way you use the C C function. See C. =item CvSTASH Returns the stash of the CV. HV* CvSTASH( SV* sv ) =item PL_DBsingle When Perl is run in debugging mode, with the B<-d> switch, this SV is a boolean which indicates whether subs are being single-stepped. Single-stepping is automatically turned on after every step. This is the C variable which corresponds to Perl's $DB::single variable. See C. =item PL_DBsub When Perl is run in debugging mode, with the B<-d> switch, this GV contains the SV which holds the name of the sub being debugged. This is the C variable which corresponds to Perl's $DB::sub variable. See C. The sub name can be found by SvPV( GvSV( PL_DBsub ), PL_na ) =item PL_DBtrace Trace variable used when Perl is run in debugging mode, with the B<-d> switch. This is the C variable which corresponds to Perl's $DB::trace variable. See C. =item dMARK Declare a stack marker variable, C, for the XSUB. See C and C. =item dORIGMARK Saves the original stack mark for the XSUB. See C. =item PL_dowarn The C variable which corresponds to Perl's $^W warning variable. =item dSP Declares a local copy of perl's stack pointer for the XSUB, available via the C macro. See C. =item dXSARGS Sets up stack and mark pointers for an XSUB, calling dSP and dMARK. This is usually handled automatically by C. Declares the C variable to indicate the number of items on the stack. =item dXSI32 Sets up the C variable for an XSUB which has aliases. This is usually handled automatically by C. =item do_binmode Switches filehandle to binmode. C is what C would contain. do_binmode(fp, iotype, TRUE); =item ENTER Opening bracket on a callback. See C and L. ENTER; =item EXTEND Used to extend the argument stack for an XSUB's return values. EXTEND( sp, int x ) =item fbm_compile Analyses the string in order to make fast searches on it using fbm_instr() -- the Boyer-Moore algorithm. void fbm_compile(SV* sv, U32 flags) =item fbm_instr Returns the location of the SV in the string delimited by C and C. It returns C if the string can't be found. The C does not have to be fbm_compiled, but the search will not be as fast then. char* fbm_instr(char *str, char *strend, SV *sv, U32 flags) =item FREETMPS Closing bracket for temporaries on a callback. See C and L. FREETMPS; =item G_ARRAY Used to indicate array context. See C, C and L. =item G_DISCARD Indicates that arguments returned from a callback should be discarded. See L. =item G_EVAL Used to force a Perl C wrapper around a callback. See L. =item GIMME A backward-compatible version of C which can only return C or C; in a void context, it returns C. =item GIMME_V The XSUB-writer's equivalent to Perl's C. Returns C, C or C for void, scalar or array context, respectively. =item G_NOARGS Indicates that no arguments are being sent to a callback. See L. =item G_SCALAR Used to indicate scalar context. See C, C, and L. =item gv_fetchmeth Returns the glob with the given C and a defined subroutine or C. The glob lives in the given C, or in the stashes accessible via @ISA and @UNIVERSAL. The argument C should be either 0 or -1. If C, as a side-effect creates a glob with the given C in the given C which in the case of success contains an alias for the subroutine, and sets up caching info for this glob. Similarly for all the searched stashes. This function grants C<"SUPER"> token as a postfix of the stash name. The GV returned from C may be a method cache entry, which is not visible to Perl code. So when calling C, you should not use the GV directly; instead, you should use the method's CV, which can be obtained from the GV with the C macro. GV* gv_fetchmeth (HV* stash, char* name, STRLEN len, I32 level) =item gv_fetchmethod =item gv_fetchmethod_autoload Returns the glob which contains the subroutine to call to invoke the method on the C. In fact in the presense of autoloading this may be the glob for "AUTOLOAD". In this case the corresponding variable $AUTOLOAD is already setup. The third parameter of C determines whether AUTOLOAD lookup is performed if the given method is not present: non-zero means yes, look for AUTOLOAD; zero means no, don't look for AUTOLOAD. Calling C is equivalent to calling C with a non-zero C parameter. These functions grant C<"SUPER"> token as a prefix of the method name. Note that if you want to keep the returned glob for a long time, you need to check for it being "AUTOLOAD", since at the later time the call may load a different subroutine due to $AUTOLOAD changing its value. Use the glob created via a side effect to do this. These functions have the same side-effects and as C with C. C should be writable if contains C<':'> or C<'\''>. The warning against passing the GV returned by C to C apply equally to these functions. GV* gv_fetchmethod (HV* stash, char* name) GV* gv_fetchmethod_autoload (HV* stash, char* name, I32 autoload) =item G_VOID Used to indicate void context. See C and L. =item gv_stashpv Returns a pointer to the stash for a specified package. If C is set then the package will be created if it does not already exist. If C is not set and the package does not exist then NULL is returned. HV* gv_stashpv (char* name, I32 create) =item gv_stashsv Returns a pointer to the stash for a specified package. See C. HV* gv_stashsv (SV* sv, I32 create) =item GvSV Return the SV from the GV. =item HEf_SVKEY This flag, used in the length slot of hash entries and magic structures, specifies the structure contains a C pointer where a C pointer is to be expected. (For information only--not to be used). =item HeHASH Returns the computed hash stored in the hash entry. U32 HeHASH(HE* he) =item HeKEY Returns the actual pointer stored in the key slot of the hash entry. The pointer may be either C or C, depending on the value of C. Can be assigned to. The C or C macros are usually preferable for finding the value of a key. char* HeKEY(HE* he) =item HeKLEN If this is negative, and amounts to C, it indicates the entry holds an C key. Otherwise, holds the actual length of the key. Can be assigned to. The C macro is usually preferable for finding key lengths. int HeKLEN(HE* he) =item HePV Returns the key slot of the hash entry as a C value, doing any necessary dereferencing of possibly C keys. The length of the string is placed in C (this is a macro, so do I use C<&len>). If you do not care about what the length of the key is, you may use the global variable C. Remember though, that hash keys in perl are free to contain embedded nulls, so using C or similar is not a good way to find the length of hash keys. This is very similar to the C macro described elsewhere in this document. char* HePV(HE* he, STRLEN len) =item HeSVKEY Returns the key as an C, or C if the hash entry does not contain an C key. HeSVKEY(HE* he) =item HeSVKEY_force Returns the key as an C. Will create and return a temporary mortal C if the hash entry contains only a C key. HeSVKEY_force(HE* he) =item HeSVKEY_set Sets the key to a given C, taking care to set the appropriate flags to indicate the presence of an C key, and returns the same C. HeSVKEY_set(HE* he, SV* sv) =item HeVAL Returns the value slot (type C) stored in the hash entry. HeVAL(HE* he) =item hv_clear Clears a hash, making it empty. void hv_clear (HV* tb) =item hv_delayfree_ent Releases a hash entry, such as while iterating though the hash, but delays actual freeing of key and value until the end of the current statement (or thereabouts) with C. See C and C. void hv_delayfree_ent (HV* hv, HE* entry) =item hv_delete Deletes a key/value pair in the hash. The value SV is removed from the hash and returned to the caller. The C is the length of the key. The C value will normally be zero; if set to G_DISCARD then NULL will be returned. SV* hv_delete (HV* tb, char* key, U32 klen, I32 flags) =item hv_delete_ent Deletes a key/value pair in the hash. The value SV is removed from the hash and returned to the caller. The C value will normally be zero; if set to G_DISCARD then NULL will be returned. C can be a valid precomputed hash value, or 0 to ask for it to be computed. SV* hv_delete_ent (HV* tb, SV* key, I32 flags, U32 hash) =item hv_exists Returns a boolean indicating whether the specified hash key exists. The C is the length of the key. bool hv_exists (HV* tb, char* key, U32 klen) =item hv_exists_ent Returns a boolean indicating whether the specified hash key exists. C can be a valid precomputed hash value, or 0 to ask for it to be computed. bool hv_exists_ent (HV* tb, SV* key, U32 hash) =item hv_fetch Returns the SV which corresponds to the specified key in the hash. The C is the length of the key. If C is set then the fetch will be part of a store. Check that the return value is non-null before dereferencing it to a C. See L for more information on how to use this function on tied hashes. SV** hv_fetch (HV* tb, char* key, U32 klen, I32 lval) =item hv_fetch_ent Returns the hash entry which corresponds to the specified key in the hash. C must be a valid precomputed hash number for the given C, or 0 if you want the function to compute it. IF C is set then the fetch will be part of a store. Make sure the return value is non-null before accessing it. The return value when C is a tied hash is a pointer to a static location, so be sure to make a copy of the structure if you need to store it somewhere. See L for more information on how to use this function on tied hashes. HE* hv_fetch_ent (HV* tb, SV* key, I32 lval, U32 hash) =item hv_free_ent Releases a hash entry, such as while iterating though the hash. See C and C. void hv_free_ent (HV* hv, HE* entry) =item hv_iterinit Prepares a starting point to traverse a hash table. I32 hv_iterinit (HV* tb) Returns the number of keys in the hash (i.e. the same as C). The return value is currently only meaningful for hashes without tie magic. NOTE: Before version 5.004_65, C used to return the number of hash buckets that happen to be in use. If you still need that esoteric value, you can get it through the macro C. =item hv_iterkey Returns the key from the current position of the hash iterator. See C. char* hv_iterkey (HE* entry, I32* retlen) =item hv_iterkeysv Returns the key as an C from the current position of the hash iterator. The return value will always be a mortal copy of the key. Also see C. SV* hv_iterkeysv (HE* entry) =item hv_iternext Returns entries from a hash iterator. See C. HE* hv_iternext (HV* tb) =item hv_iternextsv Performs an C, C, and C in one operation. SV* hv_iternextsv (HV* hv, char** key, I32* retlen) =item hv_iterval Returns the value from the current position of the hash iterator. See C. SV* hv_iterval (HV* tb, HE* entry) =item hv_magic Adds magic to a hash. See C. void hv_magic (HV* hv, GV* gv, int how) =item HvNAME Returns the package name of a stash. See C, C. char* HvNAME (HV* stash) =item hv_store Stores an SV in a hash. The hash key is specified as C and C is the length of the key. The C parameter is the precomputed hash value; if it is zero then Perl will compute it. The return value will be NULL if the operation failed or if the value did not need to be actually stored within the hash (as in the case of tied hashes). Otherwise it can be dereferenced to get the original C. Note that the caller is responsible for suitably incrementing the reference count of C before the call, and decrementing it if the function returned NULL. See L for more information on how to use this function on tied hashes. SV** hv_store (HV* tb, char* key, U32 klen, SV* val, U32 hash) =item hv_store_ent Stores C in a hash. The hash key is specified as C. The C parameter is the precomputed hash value; if it is zero then Perl will compute it. The return value is the new hash entry so created. It will be NULL if the operation failed or if the value did not need to be actually stored within the hash (as in the case of tied hashes). Otherwise the contents of the return value can be accessed using the C macros described here. Note that the caller is responsible for suitably incrementing the reference count of C before the call, and decrementing it if the function returned NULL. See L for more information on how to use this function on tied hashes. HE* hv_store_ent (HV* tb, SV* key, SV* val, U32 hash) =item hv_undef Undefines the hash. void hv_undef (HV* tb) =item isALNUM Returns a boolean indicating whether the C C is an ascii alphanumeric character or digit. int isALNUM (char c) =item isALPHA Returns a boolean indicating whether the C C is an ascii alphabetic character. int isALPHA (char c) =item isDIGIT Returns a boolean indicating whether the C C is an ascii digit. int isDIGIT (char c) =item isLOWER Returns a boolean indicating whether the C C is a lowercase character. int isLOWER (char c) =item isSPACE Returns a boolean indicating whether the C C is whitespace. int isSPACE (char c) =item isUPPER Returns a boolean indicating whether the C C is an uppercase character. int isUPPER (char c) =item items Variable which is setup by C to indicate the number of items on the stack. See L. =item ix Variable which is setup by C to indicate which of an XSUB's aliases was used to invoke it. See L. =item LEAVE Closing bracket on a callback. See C and L. LEAVE; =item looks_like_number Test if an the content of an SV looks like a number (or is a number). int looks_like_number(SV*) =item MARK Stack marker variable for the XSUB. See C. =item mg_clear Clear something magical that the SV represents. See C. int mg_clear (SV* sv) =item mg_copy Copies the magic from one SV to another. See C. int mg_copy (SV *, SV *, char *, STRLEN) =item mg_find Finds the magic pointer for type matching the SV. See C. MAGIC* mg_find (SV* sv, int type) =item mg_free Free any magic storage used by the SV. See C. int mg_free (SV* sv) =item mg_get Do magic after a value is retrieved from the SV. See C. int mg_get (SV* sv) =item mg_len Report on the SV's length. See C. U32 mg_len (SV* sv) =item mg_magical Turns on the magical status of an SV. See C. void mg_magical (SV* sv) =item mg_set Do magic after a value is assigned to the SV. See C. int mg_set (SV* sv) =item Move The XSUB-writer's interface to the C C function. The C is the source, C is the destination, C is the number of items, and C is the type. Can do overlapping moves. See also C. void Move( s, d, n, t ) =item PL_na A variable which may be used with C to tell Perl to calculate the string length. =item New The XSUB-writer's interface to the C C function. void* New( x, void *ptr, int size, type ) =item newAV Creates a new AV. The reference count is set to 1. AV* newAV (void) =item Newc The XSUB-writer's interface to the C C function, with cast. void* Newc( x, void *ptr, int size, type, cast ) =item newCONSTSUB Creates a constant sub equivalent to Perl C which is eligible for inlining at compile-time. void newCONSTSUB(HV* stash, char* name, SV* sv) =item newHV Creates a new HV. The reference count is set to 1. HV* newHV (void) =item newRV_inc Creates an RV wrapper for an SV. The reference count for the original SV is incremented. SV* newRV_inc (SV* ref) For historical reasons, "newRV" is a synonym for "newRV_inc". =item newRV_noinc Creates an RV wrapper for an SV. The reference count for the original SV is B incremented. SV* newRV_noinc (SV* ref) =item NEWSV Creates a new SV. A non-zero C parameter indicates the number of bytes of preallocated string space the SV should have. An extra byte for a tailing NUL is also reserved. (SvPOK is not set for the SV even if string space is allocated.) The reference count for the new SV is set to 1. C is an integer id between 0 and 1299 (used to identify leaks). SV* NEWSV (int id, STRLEN len) =item newSViv Creates a new SV and copies an integer into it. The reference count for the SV is set to 1. SV* newSViv (IV i) =item newSVnv Creates a new SV and copies a double into it. The reference count for the SV is set to 1. SV* newSVnv (NV i) =item newSVpv Creates a new SV and copies a string into it. The reference count for the SV is set to 1. If C is zero then Perl will compute the length. SV* newSVpv (char* s, STRLEN len) =item newSVpvf Creates a new SV an initialize it with the string formatted like C. SV* newSVpvf(const char* pat, ...); =item newSVpvn Creates a new SV and copies a string into it. The reference count for the SV is set to 1. If C is zero then Perl will create a zero length string. SV* newSVpvn (char* s, STRLEN len) =item newSVrv Creates a new SV for the RV, C, to point to. If C is not an RV then it will be upgraded to one. If C is non-null then the new SV will be blessed in the specified package. The new SV is returned and its reference count is 1. SV* newSVrv (SV* rv, char* classname) =item newSVsv Creates a new SV which is an exact duplicate of the original SV. SV* newSVsv (SV* old) =item newXS Used by C to hook up XSUBs as Perl subs. =item newXSproto Used by C to hook up XSUBs as Perl subs. Adds Perl prototypes to the subs. =item Newz The XSUB-writer's interface to the C C function. The allocated memory is zeroed with C. void* Newz( x, void *ptr, int size, type ) =item Nullav Null AV pointer. =item Nullch Null character pointer. =item Nullcv Null CV pointer. =item Nullhv Null HV pointer. =item Nullsv Null SV pointer. =item ORIGMARK The original stack mark for the XSUB. See C. =item perl_alloc Allocates a new Perl interpreter. See L. =item perl_call_argv Performs a callback to the specified Perl sub. See L. I32 perl_call_argv (char* subname, I32 flags, char** argv) =item perl_call_method Performs a callback to the specified Perl method. The blessed object must be on the stack. See L. I32 perl_call_method (char* methname, I32 flags) =item perl_call_pv Performs a callback to the specified Perl sub. See L. I32 perl_call_pv (char* subname, I32 flags) =item perl_call_sv Performs a callback to the Perl sub whose name is in the SV. See L. I32 perl_call_sv (SV* sv, I32 flags) =item perl_construct Initializes a new Perl interpreter. See L. =item perl_destruct Shuts down a Perl interpreter. See L. =item perl_eval_sv Tells Perl to C the string in the SV. I32 perl_eval_sv (SV* sv, I32 flags) =item perl_eval_pv Tells Perl to C the given string and return an SV* result. SV* perl_eval_pv (char* p, I32 croak_on_error) =item perl_free Releases a Perl interpreter. See L. =item perl_get_av Returns the AV of the specified Perl array. If C is set and the Perl variable does not exist then it will be created. If C is not set and the variable does not exist then NULL is returned. AV* perl_get_av (char* name, I32 create) =item perl_get_cv Returns the CV of the specified Perl sub. If C is set and the Perl variable does not exist then it will be created. If C is not set and the variable does not exist then NULL is returned. CV* perl_get_cv (char* name, I32 create) =item perl_get_hv Returns the HV of the specified Perl hash. If C is set and the Perl variable does not exist then it will be created. If C is not set and the variable does not exist then NULL is returned. HV* perl_get_hv (char* name, I32 create) =item perl_get_sv Returns the SV of the specified Perl scalar. If C is set and the Perl variable does not exist then it will be created. If C is not set and the variable does not exist then NULL is returned. SV* perl_get_sv (char* name, I32 create) =item perl_parse Tells a Perl interpreter to parse a Perl script. See L. =item perl_require_pv Tells Perl to C a module. void perl_require_pv (char* pv) =item perl_run Tells a Perl interpreter to run. See L. =item POPi Pops an integer off the stack. int POPi() =item POPl Pops a long off the stack. long POPl() =item POPp Pops a string off the stack. char* POPp() =item POPn Pops a double off the stack. double POPn() =item POPs Pops an SV off the stack. SV* POPs() =item PUSHMARK Opening bracket for arguments on a callback. See C and L. PUSHMARK(p) =item PUSHi Push an integer onto the stack. The stack must have room for this element. Handles 'set' magic. See C. void PUSHi(int d) =item PUSHn Push a double onto the stack. The stack must have room for this element. Handles 'set' magic. See C. void PUSHn(double d) =item PUSHp Push a string onto the stack. The stack must have room for this element. The C indicates the length of the string. Handles 'set' magic. See C. void PUSHp(char *c, int len ) =item PUSHs Push an SV onto the stack. The stack must have room for this element. Does not handle 'set' magic. See C. void PUSHs(sv) =item PUSHu Push an unsigned integer onto the stack. The stack must have room for this element. See C. void PUSHu(unsigned int d) =item PUTBACK Closing bracket for XSUB arguments. This is usually handled by C. See C and L for other uses. PUTBACK; =item Renew The XSUB-writer's interface to the C C function. void* Renew( void *ptr, int size, type ) =item Renewc The XSUB-writer's interface to the C C function, with cast. void* Renewc( void *ptr, int size, type, cast ) =item RETVAL Variable which is setup by C to hold the return value for an XSUB. This is always the proper type for the XSUB. See L. =item safefree The XSUB-writer's interface to the C C function. =item safemalloc The XSUB-writer's interface to the C C function. =item saferealloc The XSUB-writer's interface to the C C function. =item savepv Copy a string to a safe spot. This does not use an SV. char* savepv (char* sv) =item savepvn Copy a string to a safe spot. The C indicates number of bytes to copy. This does not use an SV. char* savepvn (char* sv, I32 len) =item SAVETMPS Opening bracket for temporaries on a callback. See C and L. SAVETMPS; =item SP Stack pointer. This is usually handled by C. See C and C. =item SPAGAIN Refetch the stack pointer. Used after a callback. See L. SPAGAIN; =item ST Used to access elements on the XSUB's stack. SV* ST(int x) =item strEQ Test two strings to see if they are equal. Returns true or false. int strEQ( char *s1, char *s2 ) =item strGE Test two strings to see if the first, C, is greater than or equal to the second, C. Returns true or false. int strGE( char *s1, char *s2 ) =item strGT Test two strings to see if the first, C, is greater than the second, C. Returns true or false. int strGT( char *s1, char *s2 ) =item strLE Test two strings to see if the first, C, is less than or equal to the second, C. Returns true or false. int strLE( char *s1, char *s2 ) =item strLT Test two strings to see if the first, C, is less than the second, C. Returns true or false. int strLT( char *s1, char *s2 ) =item strNE Test two strings to see if they are different. Returns true or false. int strNE( char *s1, char *s2 ) =item strnEQ Test two strings to see if they are equal. The C parameter indicates the number of bytes to compare. Returns true or false. int strnEQ( char *s1, char *s2 ) =item strnNE Test two strings to see if they are different. The C parameter indicates the number of bytes to compare. Returns true or false. int strnNE( char *s1, char *s2, int len ) =item sv_2mortal Marks an SV as mortal. The SV will be destroyed when the current context ends. SV* sv_2mortal (SV* sv) =item sv_bless Blesses an SV into a specified package. The SV must be an RV. The package must be designated by its stash (see C). The reference count of the SV is unaffected. SV* sv_bless (SV* sv, HV* stash) =item sv_catpv Concatenates the string onto the end of the string which is in the SV. Handles 'get' magic, but not 'set' magic. See C. void sv_catpv (SV* sv, char* ptr) =item sv_catpv_mg Like C, but also handles 'set' magic. void sv_catpvn (SV* sv, char* ptr) =item sv_catpvn Concatenates the string onto the end of the string which is in the SV. The C indicates number of bytes to copy. Handles 'get' magic, but not 'set' magic. See C. void sv_catpvn (SV* sv, char* ptr, STRLEN len) =item sv_catpvn_mg Like C, but also handles 'set' magic. void sv_catpvn_mg (SV* sv, char* ptr, STRLEN len) =item sv_catpvf Processes its arguments like C and appends the formatted output to an SV. Handles 'get' magic, but not 'set' magic. C must typically be called after calling this function to handle 'set' magic. void sv_catpvf (SV* sv, const char* pat, ...) =item sv_catpvf_mg Like C, but also handles 'set' magic. void sv_catpvf_mg (SV* sv, const char* pat, ...) =item sv_catsv Concatenates the string from SV C onto the end of the string in SV C. Handles 'get' magic, but not 'set' magic. See C. void sv_catsv (SV* dsv, SV* ssv) =item sv_catsv_mg Like C, but also handles 'set' magic. void sv_catsv_mg (SV* dsv, SV* ssv) =item sv_chop Efficient removal of characters from the beginning of the string buffer. SvPOK(sv) must be true and the C must be a pointer to somewhere inside the string buffer. The C becomes the first character of the adjusted string. void sv_chop(SV* sv, char *ptr) =item sv_cmp Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the string in C is less than, equal to, or greater than the string in C. I32 sv_cmp (SV* sv1, SV* sv2) =item SvCUR Returns the length of the string which is in the SV. See C. int SvCUR (SV* sv) =item SvCUR_set Set the length of the string which is in the SV. See C. void SvCUR_set (SV* sv, int val ) =item sv_dec Auto-decrement of the value in the SV. void sv_dec (SV* sv) =item sv_derived_from Returns a boolean indicating whether the SV is a subclass of the specified class. int sv_derived_from(SV* sv, char* class) =item sv_derived_from Returns a boolean indicating whether the SV is derived from the specified class. This is the function that implements C. It works for class names as well as for objects. bool sv_derived_from _((SV* sv, char* name)); =item SvEND Returns a pointer to the last character in the string which is in the SV. See C. Access the character as char* SvEND(sv) =item sv_eq Returns a boolean indicating whether the strings in the two SVs are identical. I32 sv_eq (SV* sv1, SV* sv2) =item SvGETMAGIC Invokes C on an SV if it has 'get' magic. This macro evaluates its argument more than once. void SvGETMAGIC( SV *sv ) =item SvGROW Expands the character buffer in the SV so that it has room for the indicated number of bytes (remember to reserve space for an extra trailing NUL character). Calls C to perform the expansion if necessary. Returns a pointer to the character buffer. char* SvGROW( SV* sv, int len ) =item sv_grow Expands the character buffer in the SV. This will use C and will upgrade the SV to C. Returns a pointer to the character buffer. Use C. =item sv_inc Auto-increment of the value in the SV. void sv_inc (SV* sv) =item sv_insert Inserts a string at the specified offset/length within the SV. Similar to the Perl substr() function. void sv_insert(SV *sv, STRLEN offset, STRLEN len, char *str, STRLEN strlen) =item SvIOK Returns a boolean indicating whether the SV contains an integer. int SvIOK (SV* SV) =item SvIOK_off Unsets the IV status of an SV. void SvIOK_off (SV* sv) =item SvIOK_on Tells an SV that it is an integer. void SvIOK_on (SV* sv) =item SvIOK_only Tells an SV that it is an integer and disables all other OK bits. void SvIOK_only (SV* sv) =item SvIOKp Returns a boolean indicating whether the SV contains an integer. Checks the B setting. Use C. int SvIOKp (SV* SV) =item sv_isa Returns a boolean indicating whether the SV is blessed into the specified class. This does not check for subtypes; use C to verify an inheritance relationship. int sv_isa (SV* sv, char* name) =item sv_isobject Returns a boolean indicating whether the SV is an RV pointing to a blessed object. If the SV is not an RV, or if the object is not blessed, then this will return false. int sv_isobject (SV* sv) =item SvIV Returns the integer which is in the SV. int SvIV (SV* sv) =item SvIVX Returns the integer which is stored in the SV. int SvIVX (SV* sv) =item SvLEN Returns the size of the string buffer in the SV. See C. int SvLEN (SV* sv) =item sv_len Returns the length of the string in the SV. Use C. STRLEN sv_len (SV* sv) =item sv_magic Adds magic to an SV. void sv_magic (SV* sv, SV* obj, int how, char* name, I32 namlen) =item sv_mortalcopy Creates a new SV which is a copy of the original SV. The new SV is marked as mortal. SV* sv_mortalcopy (SV* oldsv) =item sv_newmortal Creates a new SV which is mortal. The reference count of the SV is set to 1. SV* sv_newmortal (void) =item SvNIOK Returns a boolean indicating whether the SV contains a number, integer or double. int SvNIOK (SV* SV) =item SvNIOK_off Unsets the NV/IV status of an SV. void SvNIOK_off (SV* sv) =item SvNIOKp Returns a boolean indicating whether the SV contains a number, integer or double. Checks the B setting. Use C. int SvNIOKp (SV* SV) =item PL_sv_no This is the C SV. See C. Always refer to this as C<&PL_sv_no>. =item SvNOK Returns a boolean indicating whether the SV contains a double. int SvNOK (SV* SV) =item SvNOK_off Unsets the NV status of an SV. void SvNOK_off (SV* sv) =item SvNOK_on Tells an SV that it is a double. void SvNOK_on (SV* sv) =item SvNOK_only Tells an SV that it is a double and disables all other OK bits. void SvNOK_only (SV* sv) =item SvNOKp Returns a boolean indicating whether the SV contains a double. Checks the B setting. Use C. int SvNOKp (SV* SV) =item SvNV Returns the double which is stored in the SV. double SvNV (SV* sv) =item SvNVX Returns the double which is stored in the SV. double SvNVX (SV* sv) =item SvOK Returns a boolean indicating whether the value is an SV. int SvOK (SV* sv) =item SvOOK Returns a boolean indicating whether the SvIVX is a valid offset value for the SvPVX. This hack is used internally to speed up removal of characters from the beginning of a SvPV. When SvOOK is true, then the start of the allocated string buffer is really (SvPVX - SvIVX). int SvOOK(SV* sv) =item SvPOK Returns a boolean indicating whether the SV contains a character string. int SvPOK (SV* SV) =item SvPOK_off Unsets the PV status of an SV. void SvPOK_off (SV* sv) =item SvPOK_on Tells an SV that it is a string. void SvPOK_on (SV* sv) =item SvPOK_only Tells an SV that it is a string and disables all other OK bits. void SvPOK_only (SV* sv) =item SvPOKp Returns a boolean indicating whether the SV contains a character string. Checks the B setting. Use C. int SvPOKp (SV* SV) =item SvPV Returns a pointer to the string in the SV, or a stringified form of the SV if the SV does not contain a string. If C is C then Perl will handle the length on its own. Handles 'get' magic. char* SvPV (SV* sv, int len ) =item SvPV_force Like but will force the SV into becoming a string (SvPOK). You want force if you are going to update the SvPVX directly. char* SvPV_force(SV* sv, int len) =item SvPVX Returns a pointer to the string in the SV. The SV must contain a string. char* SvPVX (SV* sv) =item SvREFCNT Returns the value of the object's reference count. int SvREFCNT (SV* sv) =item SvREFCNT_dec Decrements the reference count of the given SV. void SvREFCNT_dec (SV* sv) =item SvREFCNT_inc Increments the reference count of the given SV. void SvREFCNT_inc (SV* sv) =item SvROK Tests if the SV is an RV. int SvROK (SV* sv) =item SvROK_off Unsets the RV status of an SV. void SvROK_off (SV* sv) =item SvROK_on Tells an SV that it is an RV. void SvROK_on (SV* sv) =item SvRV Dereferences an RV to return the SV. SV* SvRV (SV* sv) =item SvSETMAGIC Invokes C on an SV if it has 'set' magic. This macro evaluates its argument more than once. void SvSETMAGIC( SV *sv ) =item sv_setiv Copies an integer into the given SV. Does not handle 'set' magic. See C. void sv_setiv (SV* sv, IV num) =item sv_setiv_mg Like C, but also handles 'set' magic. void sv_setiv_mg (SV* sv, IV num) =item sv_setnv Copies a double into the given SV. Does not handle 'set' magic. See C. void sv_setnv (SV* sv, double num) =item sv_setnv_mg Like C, but also handles 'set' magic. void sv_setnv_mg (SV* sv, double num) =item sv_setpv Copies a string into an SV. The string must be null-terminated. Does not handle 'set' magic. See C. void sv_setpv (SV* sv, char* ptr) =item sv_setpv_mg Like C, but also handles 'set' magic. void sv_setpv_mg (SV* sv, char* ptr) =item sv_setpviv Copies an integer into the given SV, also updating its string value. Does not handle 'set' magic. See C. void sv_setpviv (SV* sv, IV num) =item sv_setpviv_mg Like C, but also handles 'set' magic. void sv_setpviv_mg (SV* sv, IV num) =item sv_setpvn Copies a string into an SV. The C parameter indicates the number of bytes to be copied. Does not handle 'set' magic. See C. void sv_setpvn (SV* sv, char* ptr, STRLEN len) =item sv_setpvn_mg Like C, but also handles 'set' magic. void sv_setpvn_mg (SV* sv, char* ptr, STRLEN len) =item sv_setpvf Processes its arguments like C and sets an SV to the formatted output. Does not handle 'set' magic. See C. void sv_setpvf (SV* sv, const char* pat, ...) =item sv_setpvf_mg Like C, but also handles 'set' magic. void sv_setpvf_mg (SV* sv, const char* pat, ...) =item sv_setref_iv Copies an integer into a new SV, optionally blessing the SV. The C argument will be upgraded to an RV. That RV will be modified to point to the new SV. The C argument indicates the package for the blessing. Set C to C to avoid the blessing. The new SV will be returned and will have a reference count of 1. SV* sv_setref_iv (SV *rv, char *classname, IV iv) =item sv_setref_nv Copies a double into a new SV, optionally blessing the SV. The C argument will be upgraded to an RV. That RV will be modified to point to the new SV. The C argument indicates the package for the blessing. Set C to C to avoid the blessing. The new SV will be returned and will have a reference count of 1. SV* sv_setref_nv (SV *rv, char *classname, double nv) =item sv_setref_pv Copies a pointer into a new SV, optionally blessing the SV. The C argument will be upgraded to an RV. That RV will be modified to point to the new SV. If the C argument is NULL then C will be placed into the SV. The C argument indicates the package for the blessing. Set C to C to avoid the blessing. The new SV will be returned and will have a reference count of 1. SV* sv_setref_pv (SV *rv, char *classname, void* pv) Do not use with integral Perl types such as HV, AV, SV, CV, because those objects will become corrupted by the pointer copy process. Note that C copies the string while this copies the pointer. =item sv_setref_pvn Copies a string into a new SV, optionally blessing the SV. The length of the string must be specified with C. The C argument will be upgraded to an RV. That RV will be modified to point to the new SV. The C argument indicates the package for the blessing. Set C to C to avoid the blessing. The new SV will be returned and will have a reference count of 1. SV* sv_setref_pvn (SV *rv, char *classname, char* pv, I32 n) Note that C copies the pointer while this copies the string. =item SvSetSV Calls C if dsv is not the same as ssv. May evaluate arguments more than once. void SvSetSV (SV* dsv, SV* ssv) =item SvSetSV_nosteal Calls a non-destructive version of C if dsv is not the same as ssv. May evaluate arguments more than once. void SvSetSV_nosteal (SV* dsv, SV* ssv) =item sv_setsv Copies the contents of the source SV C into the destination SV C. The source SV may be destroyed if it is mortal. Does not handle 'set' magic. See the macro forms C, C and C. void sv_setsv (SV* dsv, SV* ssv) =item sv_setsv_mg Like C, but also handles 'set' magic. void sv_setsv_mg (SV* dsv, SV* ssv) =item sv_setuv Copies an unsigned integer into the given SV. Does not handle 'set' magic. See C. void sv_setuv (SV* sv, UV num) =item sv_setuv_mg Like C, but also handles 'set' magic. void sv_setuv_mg (SV* sv, UV num) =item SvSTASH Returns the stash of the SV. HV* SvSTASH (SV* sv) =item SvTAINT Taints an SV if tainting is enabled void SvTAINT (SV* sv) =item SvTAINTED Checks to see if an SV is tainted. Returns TRUE if it is, FALSE if not. int SvTAINTED (SV* sv) =item SvTAINTED_off Untaints an SV. Be I careful with this routine, as it short-circuits some of Perl's fundamental security features. XS module authors should not use this function unless they fully understand all the implications of unconditionally untainting the value. Untainting should be done in the standard perl fashion, via a carefully crafted regexp, rather than directly untainting variables. void SvTAINTED_off (SV* sv) =item SvTAINTED_on Marks an SV as tainted. void SvTAINTED_on (SV* sv) =item SVt_IV Integer type flag for scalars. See C. =item SVt_PV Pointer type flag for scalars. See C. =item SVt_PVAV Type flag for arrays. See C. =item SVt_PVCV Type flag for code refs. See C. =item SVt_PVHV Type flag for hashes. See C. =item SVt_PVMG Type flag for blessed scalars. See C. =item SVt_NV Double type flag for scalars. See C. =item SvTRUE Returns a boolean indicating whether Perl would evaluate the SV as true or false, defined or undefined. Does not handle 'get' magic. int SvTRUE (SV* sv) =item SvTYPE Returns the type of the SV. See C. svtype SvTYPE (SV* sv) =item svtype An enum of flags for Perl types. These are found in the file B in the C enum. Test these flags with the C macro. =item PL_sv_undef This is the C SV. Always refer to this as C<&PL_sv_undef>. =item sv_unref Unsets the RV status of the SV, and decrements the reference count of whatever was being referenced by the RV. This can almost be thought of as a reversal of C. See C. void sv_unref (SV* sv) =item SvUPGRADE Used to upgrade an SV to a more complex form. Uses C to perform the upgrade if necessary. See C. bool SvUPGRADE (SV* sv, svtype mt) =item sv_upgrade Upgrade an SV to a more complex form. Use C. See C. =item sv_usepvn Tells an SV to use C to find its string value. Normally the string is stored inside the SV but sv_usepvn allows the SV to use an outside string. The C should point to memory that was allocated by C. The string length, C, must be supplied. This function will realloc the memory pointed to by C, so that pointer should not be freed or used by the programmer after giving it to sv_usepvn. Does not handle 'set' magic. See C. void sv_usepvn (SV* sv, char* ptr, STRLEN len) =item sv_usepvn_mg Like C, but also handles 'set' magic. void sv_usepvn_mg (SV* sv, char* ptr, STRLEN len) =item sv_vcatpvfn(sv, pat, patlen, args, svargs, svmax, used_locale) Processes its arguments like C and appends the formatted output to an SV. Uses an array of SVs if the C style variable argument list is missing (NULL). Indicates if locale information has been used for formatting. void sv_catpvfn _((SV* sv, const char* pat, STRLEN patlen, va_list *args, SV **svargs, I32 svmax, bool *used_locale)); =item sv_vsetpvfn(sv, pat, patlen, args, svargs, svmax, used_locale) Works like C but copies the text into the SV instead of appending it. void sv_setpvfn _((SV* sv, const char* pat, STRLEN patlen, va_list *args, SV **svargs, I32 svmax, bool *used_locale)); =item SvUV Returns the unsigned integer which is in the SV. UV SvUV(SV* sv) =item SvUVX Returns the unsigned integer which is stored in the SV. UV SvUVX(SV* sv) =item PL_sv_yes This is the C SV. See C. Always refer to this as C<&PL_sv_yes>. =item THIS Variable which is setup by C to designate the object in a C++ XSUB. This is always the proper type for the C++ object. See C and L. =item toLOWER Converts the specified character to lowercase. int toLOWER (char c) =item toUPPER Converts the specified character to uppercase. int toUPPER (char c) =item warn This is the XSUB-writer's interface to Perl's C function. Use this function the same way you use the C C function. See C. =item XPUSHi Push an integer onto the stack, extending the stack if necessary. Handles 'set' magic. See C. XPUSHi(int d) =item XPUSHn Push a double onto the stack, extending the stack if necessary. Handles 'set' magic. See C. XPUSHn(double d) =item XPUSHp Push a string onto the stack, extending the stack if necessary. The C indicates the length of the string. Handles 'set' magic. See C. XPUSHp(char *c, int len) =item XPUSHs Push an SV onto the stack, extending the stack if necessary. Does not handle 'set' magic. See C. XPUSHs(sv) =item XPUSHu Push an unsigned integer onto the stack, extending the stack if necessary. See C. =item XS Macro to declare an XSUB and its C parameter list. This is handled by C. =item XSRETURN Return from XSUB, indicating number of items on the stack. This is usually handled by C. XSRETURN(int x) =item XSRETURN_EMPTY Return an empty list from an XSUB immediately. XSRETURN_EMPTY; =item XSRETURN_IV Return an integer from an XSUB immediately. Uses C. XSRETURN_IV(IV v) =item XSRETURN_NO Return C<&PL_sv_no> from an XSUB immediately. Uses C. XSRETURN_NO; =item XSRETURN_NV Return an double from an XSUB immediately. Uses C. XSRETURN_NV(NV v) =item XSRETURN_PV Return a copy of a string from an XSUB immediately. Uses C. XSRETURN_PV(char *v) =item XSRETURN_UNDEF Return C<&PL_sv_undef> from an XSUB immediately. Uses C. XSRETURN_UNDEF; =item XSRETURN_YES Return C<&PL_sv_yes> from an XSUB immediately. Uses C. XSRETURN_YES; =item XST_mIV Place an integer into the specified position C on the stack. The value is stored in a new mortal SV. XST_mIV( int i, IV v ) =item XST_mNV Place a double into the specified position C on the stack. The value is stored in a new mortal SV. XST_mNV( int i, NV v ) =item XST_mNO Place C<&PL_sv_no> into the specified position C on the stack. XST_mNO( int i ) =item XST_mPV Place a copy of a string into the specified position C on the stack. The value is stored in a new mortal SV. XST_mPV( int i, char *v ) =item XST_mUNDEF Place C<&PL_sv_undef> into the specified position C on the stack. XST_mUNDEF( int i ) =item XST_mYES Place C<&PL_sv_yes> into the specified position C on the stack. XST_mYES( int i ) =item XS_VERSION The version identifier for an XS module. This is usually handled automatically by C. See C. =item XS_VERSION_BOOTCHECK Macro to verify that a PM module's $VERSION variable matches the XS module's C variable. This is usually handled automatically by C. See L. =item Zero The XSUB-writer's interface to the C C function. The C is the destination, C is the number of items, and C is the type. void Zero( d, n, t ) =back =head1 AUTHORS Until May 1997, this document was maintained by Jeff Okamoto . It is now maintained as part of Perl itself. With lots of help and suggestions from Dean Roehrich, Malcolm Beattie, Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil Bowers, Matthew Green, Tim Bunce, Spider Boardman, Ulrich Pfeifer, Stephen McCamant, and Gurusamy Sarathy. API Listing originally by Dean Roehrich .