perlguts

# NAME

perlguts - Perl's Internal Functions

# 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.

# 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.

## What is an ``IV''?

Perl uses a special typedef IV which is large enough to hold either an integer or a pointer.

Perl also uses two special typedefs, I32 and I16, which will always be at least 32-bits and 16-bits long, respectively.

## Working with SV's

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 four routines are:

        SV*  newSViv(IV);
        SV*  newSVnv(double);
        SV*  newSVpv(char*, int);
        SV*  newSVsv(SV*);

To change the value of an *already-existing* SV, there are five routines:

        void  sv_setiv(SV*, IV);
        void  sv_setnv(SV*, double);
        void  sv_setpvn(SV*, char*, int)
        void  sv_setpv(SV*, char*);
        void  sv_setsv(SV*, SV*);

Notice that you can choose to specify the length of the string to be assigned by using sv_setpvn or newSVpv , or you may allow Perl to calculate the length by using sv_setpv or by specifying 0 as the second argument to newSVpv . Be warned, though, that Perl will determine the string's length by using `strlen`, which depends on the string terminating with a NUL character.

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 SvPV macro, the length of the string returned is placed into the variable `len` (this is a macro, so you do not use `&len`). If you do not care what the length of the data is, use the global variable na . Remember, however, that Perl allows arbitrary strings of data that may both contain NUL's and not be terminated by a NUL.

If you simply 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 `sv_grow`. Note that SvGROW can only increase, not decrease, the allocated memory of an SV.

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 SvPOK() is true.

If you want to append something to the end of string stored in an `SV*`, you can use the following functions:

        void  sv_catpv(SV*, char*);
        void  sv_catpvn(SV*, char*, int);
        void  sv_catsv(SV*, SV*);

The first function calculates the length of the string to be appended by using `strlen`. In the second, you specify the length of the string yourself. The third 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.

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("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 defined , you can call:

        SvOK(SV*)

The scalar undef value is stored in an SV instance called sv_undef . Its address can be used whenever an `SV*` is needed.

There are also the two values sv_yes and sv_no , which contain Boolean TRUE and FALSE values, respectively. Like sv_undef , their addresses can be used whenever an `SV*` is needed.

Do not be fooled into thinking that `(SV *) 0` is the same as `&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, or just weird results. Change the zero to `&sv_undef` in the first line and all will be well.

To free an SV that you've created, call SvREFCNT_dec(SV*) . Normally this call is not necessary. See the section on MORTALITY.

## What's Really Stored in an SV?

Recall that the usual method of determining the type of scalar you have is to use `Sv*OK` macros. Since a scalar can be both a number and a string, usually these macros will always return TRUE and calling the `Sv*V` macros will do the appropriate conversion of string to integer/double or integer/double to string.

If you really 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 just use the `Sv*V` macros.

## Working with AV's

There are two ways to create and load an AV. The first method just creates an empty AV:

        AV*  newAV();

The second method both creates the AV and initially populates it with SV's:

        AV*  av_make(I32 num, SV **ptr);

The second argument points to an array containing `num` `SV*`'s. Once the AV has been created, the SV's can be destroyed, if so desired.

Once the AV has been created, the following operations are possible on AV's:

        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 av_unshift . This routine adds `num` elements at the front of the array with the undef value. You must then use av_store (described below) to assign values to these new elements.

Here are some other functions:

        I32   av_len(AV*); /* Returns highest index value in array */
        SV**  av_fetch(AV*, I32 key, I32 lval);
                /* Fetches value at key offset, but it stores an undef value
                   at the offset if lval is non-zero */
        SV**  av_store(AV*, I32 key, SV* val);
                /* Stores val at offset key */

Take note that av_fetch and av_store return `SV**`'s, not `SV*`'s.

        void  av_clear(AV*);
                /* Clear out all elements, but leave the array */
        void  av_undef(AV*);
                /* Undefines the array, removing all elements */
        void  av_extend(AV*, I32 key);
                /* Extend the array to a total of key elements */

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("varname", FALSE);

This returns NULL if the variable does not exist.

## Working with HV's

To create an HV, you use the following routine:

        HV*  newHV();

Once the HV has been created, the following operations are possible on HV's:

        SV**  hv_store(HV*, char* key, U32 klen, SV* val, U32 hash);
        SV**  hv_fetch(HV*, char* key, U32 klen, I32 lval);

The `klen` parameter is the length of the key being passed in. The `val` argument contains the SV pointer to the scalar being stored, and `hash` is the pre-computed hash value (zero if you want hv_store to calculate it for you). The `lval` parameter indicates whether this fetch is actually a part of a store operation.

Remember that hv_store and hv_fetch return `SV**`'s and not just `SV*`. In order 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);

And more miscellaneous functions:

        void   hv_clear(HV*);
                /* Clears all entries in hash table */
        void   hv_undef(HV*);
                /* Undefines the hash table */

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 `SV*`. However, once you have an `HE*`, 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("varname", FALSE);

This returns NULL if the variable does not exist.

The hash algorithm, for those who are interested, is:

        i = klen;
        hash = 0;
        s = key;
        while (i--)
            hash = hash * 33 + *s++;

## References

References are a special type of scalar that point to other data types (including references).

To create a reference, use the following command:

        SV* newRV((SV*) thing);

The `thing` argument can be any of an `SV*`, `AV*`, or `HV*`. 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 `SV*` to either an `AV*` or `HV*`, if required.

To determine if an SV is a reference, you can use the following macro:

        SvROK(SV*)

To actually discover what the reference refers to, you must use the following macro and then check the value returned.

        SvTYPE(SvRV(SV*))

The most useful types that will be returned are:

        SVt_IV    Scalar
        SVt_NV    Scalar
        SVt_PV    Scalar
        SVt_PVAV  Array
        SVt_PVHV  Hash
        SVt_PVCV  Code
        SVt_PVMG  Blessed Scalar

## 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 `sv` argument must be a reference. The `stash` argument specifies which class the reference will belong to. See the section on Stashes 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 classname 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 rv. SV is blessed if classname is non-null.

            SV* sv_setref_iv(SV* rv, char* classname, IV iv);
            SV* sv_setref_nv(SV* rv, char* classname, NV iv);

Copies pointer (not a string!) into an SV whose reference is rv. SV is blessed if classname is non-null.

            SV* sv_setref_pv(SV* rv, char* classname, PV iv);

Copies string into an SV whose reference is rv. Set length to 0 to let Perl calculate the string length. SV is blessed if classname is non-null.

            SV* sv_setref_pvn(SV* rv, char* classname, PV iv, int length);
            int sv_isa(SV* sv, char* name);
            int sv_isobject(SV* sv);

# Creating New Variables

To create a new Perl variable, which can be accessed from your Perl script, use the following routines, depending on the variable type.

        SV*  perl_get_sv("varname", TRUE);
        AV*  perl_get_av("varname", TRUE);
        HV*  perl_get_hv("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 bits that may be OR'ed with the TRUE argument to enable certain extra features. Those bits are:

        0x02  Marks the variable as multiply defined, thus preventing the
              "Indentifier <varname> used only once: possible typo" warning.
        0x04  Issues a "Had to create <varname> unexpectedly" warning if
              the variable didn't actually exist.  This is useful if
              you expected the variable to already exist and want to propagate
              this warning back to the user.

If the `varname` argument does not contain a package specifier, it is created in the current package.

# XSUB's 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 ST(n) macro, which returns the `n`'th stack argument. Argument 0 is the first argument passed in the Perl subroutine call. These arguments are `SV*`, and can be used anywhere an `SV*` 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 timezone'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 `sp` is the stack pointer, and `num` 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 IV's, doubles, strings, and SV pointers respectively:

        PUSHi(IV)
        PUSHn(double)
        PUSHp(char*, I32)
        PUSHs(SV*)

And now the Perl program calling `tzname`, 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.

For more information, consult the perlxs manpage .

# Mortality

In Perl, values are normally ``immortal'' -- that is, they are not freed unless explicitly done so (via the Perl undef call or other routines in Perl itself).

Add cruft about reference counts. int SvREFCNT(SV* sv); void SvREFCNT_inc(SV* sv); void SvREFCNT_dec(SV* sv);

In the above example with `tzname`, we needed to create two new SV's to push onto the argument stack, that being the two strings. However, we don't want these new SV's to stick around forever because they will eventually be copied into the SV's that hold the two scalar variables.

An SV (or AV or HV) that is ``mortal'' acts in all ways as a normal ``immortal'' SV, AV, or HV, but is only valid in the ``current context''. When the Perl interpreter leaves the current context, the mortal SV, AV, or HV is automatically freed. Generally the ``current context'' means a single Perl statement.

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, the third creates a mortal copy of an existing SV.

The mortal routines are not just for SV's -- AV's and HV's can be made mortal by passing their address (and casting them to `SV*`) to the sv_2mortal or sv_mortalcopy routines.

>From Ilya: Beware that the sv_2mortal() call is eventually equivalent to svREFCNT_dec(). A value can happily be mortal in two different contexts, and it will be svREFCNT_dec()ed twice, once on exit from these contexts. It can also be mortal twice in the same context. This means that you should be very careful to make a value mortal exactly as many times as it is needed. The value that go to the Perl stack should be mortal.

You should be careful about creating mortal variables. It is possible for strange things to happen should you make the same value mortal within multiple contexts.

# Stashes

A stash is a hash table (associative array) 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 called a GV (for 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
        File Handle
        Directory Handle
        Format
        Subroutine

Perl stores various stashes in a separate GV structure (for global variable) but represents them with an HV structure. The keys in this larger GV are the various package names; the values are the `GV*`'s which are stashes. It may help to think of a stash purely as an HV, and that the term ``GV'' means the global variable hash.

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 `HV*`. The `create` flag will create a new package if it is set.

The name that `gv_stash*v` wants is the name of the package whose symbol table you want. The default package is called `main`. If you have multiply nested packages, pass their names to `gv_stash*v`, separated by `::` 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 return a blessed value to your Perl script, you can use the following function:

        SV*  sv_bless(SV*, HV* stash)

where the first argument, an `SV*`, must be a reference, and the second argument is a stash. The returned `SV*` can now be used in the same way as any other SV.

For more information on references and blessings, consult the perlref manpage .

# Magic

[This section still under construction. Ignore everything here. Post no bills. Everything not permitted is forbidden.]

# Version 6, 1995/1/27

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 `struct magic`'s, typedef'ed to `MAGIC`.

        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.

## 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 `sv` argument is a pointer to the SV that is to acquire a new magical feature.

If `sv` is not already magical, Perl uses the SvUPGRADE macro to set the SVt_PVMG flag for the `sv`. 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 overriden, and multiple instances of the same type of magic can be associated with an SV.

The `name` and `namlem` arguments are used to associate a string with the magic, typically the name of a variable. `namlem` is stored in the mg_len field and if `name` is non-null and `namlem` >= 0 a malloc'd copy of the name is stored in `mg_ptr` field.

The sv_magic function uses `how` to determine which, if any, predefined ``Magic Virtual Table'' should be assigned to the `mg_virtual` field. See the ``Magic Virtual Table'' section below. The `how` argument is also stored in the `mg_type` field.

The `obj` argument is stored in the `mg_obj` field of the `MAGIC` structure. If it is not the same as the `sv` argument, the reference count of the `obj` object is incremented. If it is the same, or if the `how` argument is ``#'', or if it is a null pointer, then `obj` is merely stored, without the reference count being incremented.

There is also a function to add magic to an `HV`:

        void hv_magic(HV *hv, GV *gv, int how);

This simply calls sv_magic and coerces the `gv` argument into an `SV`.

To remove the magic from an SV, call the function sv_unmagic:

        void sv_unmagic(SV *sv, int type);

The `type` argument should be equal to the `how` value when the `SV` was initially made magical.

## Magic Virtual Tables

The `mg_virtual` field in the `MAGIC` structure is a pointer to a `MGVTBL`, 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 `MGVTBL` 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 `perl.h` 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 `vtbl_sv` (which corresponds to an `mg_type` 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 `magic_get` is called. All the various routines for the various magical types begin with `magic_`.

The current kinds of Magic Virtual Tables are:

        mg_type  MGVTBL              Type of magicalness
        -------  ------              -------------------
        \0       vtbl_sv             Regexp???
        A        vtbl_amagic         Operator Overloading
        a        vtbl_amagicelem     Operator Overloading
        c        0                   Used in Operator Overloading
        B        vtbl_bm             Boyer-Moore???
        E        vtbl_env            %ENV hash
        e        vtbl_envelem        %ENV hash element
        g        vtbl_mglob          Regexp /g flag???
        I        vtbl_isa            @ISA array
        i        vtbl_isaelem        @ISA array element
        L        0 (but sets RMAGICAL)     Perl Module/Debugger???
        l        vtbl_dbline         Debugger?
        P        vtbl_pack           Tied Array or Hash
        p        vtbl_packelem       Tied Array or Hash element
        q        vtbl_packelem       Tied Scalar or Handle
        S        vtbl_sig            Signal Hash
        s        vtbl_sigelem        Signal Hash element
        t        vtbl_taint          Taintedness
        U        vtbl_uvar           ???
        v        vtbl_vec            Vector
        x        vtbl_substr         Substring???
        *        vtbl_glob           GV???
        #        vtbl_arylen         Array Length
        .        vtbl_pos            $. scalar variable
        ~        Reserved for extensions, but multiple extensions may clash

When an upper-case and lower-case letter both exist in the table, then the upper-case letter is used to represent some kind of composite type (a list or a hash), and the lower-case letter is used to represent an element of that composite type.

## Finding Magic

        MAGIC* mg_find(SV*, int type); /* Finds the magic pointer of that type */

This routine returns a pointer to the `MAGIC` structure stored in the SV. If the SV does not have that magical feature, `NULL` 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 `sv` has. If the mg_type field is an upper-case letter, then the mg_obj is copied to `nsv`, but the mg_type field is changed to be the lower-case letter.

# Double-Typed SV's

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 $! contains either the numeric value of `errno` or its string equivalent from either `strerror` or `sys_errlist[]`.

To force multiple data values into an SV, you must do two things: use the `sv_set*v` 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 `sv_set*v` routine you called first. This is because every `sv_set*v` 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 sv_setiv and sv_setpv had been reversed, then the macro SvPOK_on would need to be called instead of SvIOK_on .

# 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 perl_call_sv . The `SV*` 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 perl_call_argv ), the programmer must manipulate the Perl stack. These include the following macros and functions:

        dSP
        PUSHMARK()
        PUTBACK
        SPAGAIN
        ENTER
        SAVETMPS
        FREETMPS
        LEAVE
        XPUSH*()
        POP*()

For more information, consult the perlcall manpage .

# Memory Allocation

It is strongly 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 more quickly satisfy allocation requests. 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 `x` 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 (Larry has switched to using a run-time memory checker), so this argument can be any number.

The second argument `pointer` will point to the newly allocated memory. The third and fourth arguments `number` and `type` specify how many of the specified type of data structure should be allocated. The argument `type` is passed to `sizeof`. The final argument to Newc , `cast`, should be used if the `pointer` argument is different from the `type` argument.

Unlike the New and Newc macros, the Newz macro calls `memzero` 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 Renew and Renewc match those of New and Newc 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 `source` and `dest` arguments point to the source and destination starting points. Perl will move, copy, or zero out `number` instances of the size of the `type` data structure (using the `sizeof` function).

# 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.

AvFILL
  See av_len .

av_clear
  Clears an array, making it empty.

  - void av_clear _((AV* ar));

av_extend
  Pre-extend an array. The `key` is the index to which the array should be extended.

  - void av_extend _((AV* ar, I32 key));

av_fetch
  Returns the SV at the specified index in the array. The `key` is the index. If `lval` is set then the fetch will be part of a store. Check that the return value is non-null before dereferencing it to a `SV*`.

              SV**    av_fetch _((AV* ar, I32 key, I32 lval));

av_len
  Returns the highest index in the array. Returns -1 if the array is empty.

  - I32 av_len _((AV* ar));

av_make
  Creats 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.

              AV*     av_make _((I32 size, SV** svp));

av_pop
  Pops an SV off the end of the array. Returns `&sv_undef` if the array is empty.

              SV*     av_pop _((AV* ar));

av_push
  Pushes an SV onto the end of the array.

  - void av_push _((AV* ar, SV* val));

av_shift
  Shifts an SV off the beginning of the array.

              SV*     av_shift _((AV* ar));

av_store
  Stores an SV in an array. The array index is specified as `key`. The return value will be null if the operation failed, otherwise it can be dereferenced to get the original `SV*`.

              SV**    av_store _((AV* ar, I32 key, SV* val));

av_undef
  Undefines the array.

  - void av_undef _((AV* ar));

av_unshift
  Unshift an SV onto the beginning of the array.

  - void av_unshift _((AV* ar, I32 num));

CLASS
  Variable which is setup by `xsubpp` to indicate the class name for a C++ XS constructor. This is always a `char*`. See THIS and the perlxs manpage .

Copy
  The XSUB-writer's interface to the C `memcpy` function. The `s` is the source, `d` is the destination, `n` is the number of items, and `t` is the type.

              (void) Copy( s, d, n, t );

croak
  This is the XSUB-writer's interface to Perl's die function. Use this function the same way you use the C printf function. See warn .

CvSTASH
  Returns the stash of the CV.

              HV * CvSTASH( SV* sv )

DBsingle
  When Perl is run in debugging mode, with the -d switch, this SV is a boolean which indicates whether subs are being single-stepped. Single-stepping is automatically turned on after every step. See DBsub .

DBsub
  When Perl is run in debugging mode, with the -d switch, this GV contains the SV which holds the name of the sub being debugged. See DBsingle . The sub name can be found by

              SvPV( GvSV( DBsub ), na )

dMARK
  Declare a stack marker for the XSUB. See MARK and dORIGMARK .

dORIGMARK
  Saves the original stack mark for the XSUB. See ORIGMARK .

dSP
  Declares a stack pointer for the XSUB. See SP .

dXSARGS
  Sets up stack and mark pointers for an XSUB, calling dSP and dMARK. This is usually handled automatically by `xsubpp`. Declares the items variable to indicate the number of items on the stack.

ENTER
  Opening bracket on a callback. See LEAVE and the perlcall manpage .

              ENTER;

EXTEND
  Used to extend the argument stack for an XSUB's return values.

              EXTEND( sp, int x );

FREETMPS
  Closing bracket for temporaries on a callback. See SAVETMPS and the perlcall manpage .

              FREETMPS;

G_ARRAY
  Used to indicate array context. See GIMME and the perlcall manpage .

G_DISCARD
  Indicates that arguments returned from a callback should be discarded. See the perlcall manpage .

G_EVAL
  Used to force a Perl eval wrapper around a callback. See the perlcall manpage .

GIMME
  The XSUB-writer's equivalent to Perl's wantarray . Returns G_SCALAR or G_ARRAY for scalar or array context.

G_NOARGS
  Indicates that no arguments are being sent to a callback. See the perlcall manpage .

G_SCALAR
  Used to indicate scalar context. See GIMME and the perlcall manpage .

gv_stashpv
  Returns a pointer to the stash for a specified package. If `create` is set then the package will be created if it does not already exist. If `create` is not set and the package does not exist then NULL is returned.

              HV*     gv_stashpv _((char* name, I32 create));

gv_stashsv
  Returns a pointer to the stash for a specified package. See gv_stashpv .

              HV*     gv_stashsv _((SV* sv, I32 create));

GvSV
  Return the SV from the GV.

he_free
  Releases a hash entry from an iterator. See hv_iternext .

hv_clear
  Clears a hash, making it empty.

  - void hv_clear _((HV* tb));

hv_delete
  Deletes a key/value pair in the hash. The value SV is removed from the hash and returned to the caller. The `lken` is the length of the key. The `flags` 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));

hv_exists
  Returns a boolean indicating whether the specified hash key exists. The `lken` is the length of the key.

  - bool hv_exists _((HV* tb, char* key, U32 klen));

hv_fetch
  Returns the SV which corresponds to the specified key in the hash. The `lken` is the length of the key. If `lval` is set then the fetch will be part of a store. Check that the return value is non-null before dereferencing it to a `SV*`.

              SV**    hv_fetch _((HV* tb, char* key, U32 klen, I32 lval));

hv_iterinit
  Prepares a starting point to traverse a hash table.

  - I32 hv_iterinit _((HV* tb));

hv_iterkey
  Returns the key from the current position of the hash iterator. See hv_iterinit .

              char*   hv_iterkey _((HE* entry, I32* retlen));

hv_iternext
  Returns entries from a hash iterator. See hv_iterinit .

              HE*     hv_iternext _((HV* tb));

hv_iternextsv
  Performs an hv_iternext , hv_iterkey , and hv_iterval in one operation.

              SV *    hv_iternextsv _((HV* hv, char** key, I32* retlen));

hv_iterval
  Returns the value from the current position of the hash iterator. See hv_iterkey .

              SV*     hv_iterval _((HV* tb, HE* entry));

hv_magic
  Adds magic to a hash. See sv_magic .

  - void hv_magic _((HV* hv, GV* gv, int how));

HvNAME
  Returns the package name of a stash. See SvSTASH , CvSTASH .

              char *HvNAME (HV* stash)

hv_store
  Stores an SV in a hash. The hash key is specified as `key` and `klen` is the length of the key. The `hash` parameter is the pre-computed hash value; if it is zero then Perl will compute it. The return value will be null if the operation failed, otherwise it can be dereferenced to get the original `SV*`.

              SV**    hv_store _((HV* tb, char* key, U32 klen, SV* val, U32 hash));

hv_undef
  Undefines the hash.

  - void hv_undef _((HV* tb));

isALNUM
  Returns a boolean indicating whether the C `char` is an ascii alphanumeric character or digit.

              int isALNUM (char c)

isALPHA
  Returns a boolean indicating whether the C `char` is an ascii alphanumeric character.

              int isALPHA (char c)

isDIGIT
  Returns a boolean indicating whether the C `char` is an ascii digit.

              int isDIGIT (char c)

isLOWER
  Returns a boolean indicating whether the C `char` is a lowercase character.

              int isLOWER (char c)

isSPACE
  Returns a boolean indicating whether the C `char` is whitespace.

              int isSPACE (char c)

isUPPER
  Returns a boolean indicating whether the C `char` is an uppercase character.

              int isUPPER (char c)

items
  Variable which is setup by `xsubpp` to indicate the number of items on the stack. See the perlxs manpage .

LEAVE
  Closing bracket on a callback. See ENTER and the perlcall manpage .

              LEAVE;

MARK
  Stack marker for the XSUB. See dMARK .

mg_clear
  Clear something magical that the SV represents. See sv_magic .

  - int mg_clear _((SV* sv));

mg_copy
  Copies the magic from one SV to another. See sv_magic .

  - int mg_copy _((SV *, SV *, char *, STRLEN));

mg_find
  Finds the magic pointer for type matching the SV. See sv_magic .

              MAGIC*  mg_find _((SV* sv, int type));

mg_free
  Free any magic storage used by the SV. See sv_magic .

  - int mg_free _((SV* sv));

mg_get
  Do magic after a value is retrieved from the SV. See sv_magic .

  - int mg_get _((SV* sv));

mg_len
  Report on the SV's length. See sv_magic .

  - U32 mg_len _((SV* sv));

mg_magical
  Turns on the magical status of an SV. See sv_magic .

  - void mg_magical _((SV* sv));

mg_set
  Do magic after a value is assigned to the SV. See sv_magic .

  - int mg_set _((SV* sv));

Move
  The XSUB-writer's interface to the C `memmove` function. The `s` is the source, `d` is the destination, `n` is the number of items, and `t` is the type.

              (void) Move( s, d, n, t );

na
  A variable which may be used with SvPV to tell Perl to calculate the string length.

New
  The XSUB-writer's interface to the C `malloc` function.

              void * New( x, void *ptr, int size, type )

Newc
  The XSUB-writer's interface to the C `malloc` function, with cast.

              void * Newc( x, void *ptr, int size, type, cast )

Newz
  The XSUB-writer's interface to the C `malloc` function. The allocated memory is zeroed with `memzero`.

              void * Newz( x, void *ptr, int size, type )

newAV
  Creates a new AV. The refcount is set to 1.

              AV*     newAV _((void));

newHV
  Creates a new HV. The refcount is set to 1.

              HV*     newHV _((void));

newRV
  Creates an RV wrapper for an SV. The refcount for the original SV is incremented.

              SV*     newRV _((SV* ref));

newSV
  Creates a new SV. The `len` parameter indicates the number of bytes of pre-allocated string space the SV should have. The refcount for the new SV is set to 1.

              SV*     newSV _((STRLEN len));

newSViv
  Creates a new SV and copies an integer into it. The refcount for the SV is set to 1.

              SV*     newSViv _((IV i));

newSVnv
  Creates a new SV and copies a double into it. The refcount for the SV is set to 1.

              SV*     newSVnv _((NV i));

newSVpv
  Creates a new SV and copies a string into it. The refcount for the SV is set to 1. If `len` is zero then Perl will compute the length.

              SV*     newSVpv _((char* s, STRLEN len));

newSVrv
  Creates a new SV for the RV, `rv`, to point to. If `rv` is not an RV then it will be upgraded one. If `classname` is non-null then the new SV will be blessed in the specified package. The new SV is returned and its refcount is 1.

              SV*     newSVrv _((SV* rv, char* classname));

newSVsv
  Creates a new SV which is an exact duplicate of the orignal SV.

              SV*     newSVsv _((SV* old));

newXS
  Used by `xsubpp` to hook up XSUBs as Perl subs.

newXSproto
  Used by `xsubpp` to hook up XSUBs as Perl subs. Adds Perl prototypes to the subs.

Nullav
  Null AV pointer.

Nullch
  Null character pointer.

Nullcv
  Null CV pointer.

Nullhv
  Null HV pointer.

Nullsv
  Null SV pointer.

ORIGMARK
  The original stack mark for the XSUB. See dORIGMARK .

perl_alloc
  Allocates a new Perl interpreter. See the perlembed manpage .

perl_call_argv
  Performs a callback to the specified Perl sub. See the perlcall manpage .

  - I32 perl_call_argv _((char* subname, I32 flags, char** argv));

perl_call_method
  Performs a callback to the specified Perl method. The blessed object must be on the stack. See the perlcall manpage .

  - I32 perl_call_method _((char* methname, I32 flags));

perl_call_pv
  Performs a callback to the specified Perl sub. See the perlcall manpage .

  - I32 perl_call_pv _((char* subname, I32 flags));

perl_call_sv
  Performs a callback to the Perl sub whose name is in the SV. See the perlcall manpage .

  - I32 perl_call_sv _((SV* sv, I32 flags));

perl_construct
  Initializes a new Perl interpreter. See the perlembed manpage .

perl_destruct
  Shuts down a Perl interpreter. See the perlembed manpage .

perl_eval_sv
  Tells Perl to eval the string in the SV.

  - I32 perl_eval_sv _((SV* sv, I32 flags));

perl_free
  Releases a Perl interpreter. See the perlembed manpage .

perl_get_av
  Returns the AV of the specified Perl array. If `create` is set and the Perl variable does not exist then it will be created. If `create` is not set and the variable does not exist then null is returned.

              AV*     perl_get_av _((char* name, I32 create));

perl_get_cv
  Returns the CV of the specified Perl sub. If `create` is set and the Perl variable does not exist then it will be created. If `create` is not set and the variable does not exist then null is returned.

              CV*     perl_get_cv _((char* name, I32 create));

perl_get_hv
  Returns the HV of the specified Perl hash. If `create` is set and the Perl variable does not exist then it will be created. If `create` is not set and the variable does not exist then null is returned.

              HV*     perl_get_hv _((char* name, I32 create));

perl_get_sv
  Returns the SV of the specified Perl scalar. If `create` is set and the Perl variable does not exist then it will be created. If `create` is not set and the variable does not exist then null is returned.

              SV*     perl_get_sv _((char* name, I32 create));

perl_parse
  Tells a Perl interpreter to parse a Perl script. See the perlembed manpage .

perl_require_pv
  Tells Perl to require a module.

  - void perl_require_pv _((char* pv));

perl_run
  Tells a Perl interpreter to run. See the perlembed manpage .

POPi
  Pops an integer off the stack.

              int POPi();

POPl
  Pops a long off the stack.

              long POPl();

POPp
  Pops a string off the stack.

              char * POPp();

POPn
  Pops a double off the stack.

              double POPn();

POPs
  Pops an SV off the stack.

              SV* POPs();

PUSHMARK
  Opening bracket for arguments on a callback. See PUTBACK and the perlcall manpage .

              PUSHMARK(p)

PUSHi
  Push an integer onto the stack. The stack must have room for this element. See XPUSHi .

              PUSHi(int d)

PUSHn
  Push a double onto the stack. The stack must have room for this element. See XPUSHn .

              PUSHn(double d)

PUSHp
  Push a string onto the stack. The stack must have room for this element. The `len` indicates the length of the string. See XPUSHp .

              PUSHp(char *c, int len )

PUSHs
  Push an SV onto the stack. The stack must have room for this element. See XPUSHs .

              PUSHs(sv)

PUTBACK
  Closing bracket for XSUB arguments. This is usually handled by `xsubpp`. See PUSHMARK and the perlcall manpage for other uses.

              PUTBACK;

Renew
  The XSUB-writer's interface to the C `realloc` function.

              void * Renew( void *ptr, int size, type )

Renewc
  The XSUB-writer's interface to the C `realloc` function, with cast.

              void * Renewc( void *ptr, int size, type, cast )

RETVAL
  Variable which is setup by `xsubpp` to hold the return value for an XSUB. This is always the proper type for the XSUB. See the perlxs manpage .

safefree
  The XSUB-writer's interface to the C `free` function.

safemalloc
  The XSUB-writer's interface to the C `malloc` function.

saferealloc
  The XSUB-writer's interface to the C `realloc` function.

savepv
  Copy a string to a safe spot. This does not use an SV.

              char*   savepv _((char* sv));

savepvn
  Copy a string to a safe spot. The `len` indicates number of bytes to copy. This does not use an SV.

              char*   savepvn _((char* sv, I32 len));

SAVETMPS
  Opening bracket for temporaries on a callback. See FREETMPS and the perlcall manpage .

              SAVETMPS;

SP
  Stack pointer. This is usually handled by `xsubpp`. See dSP and SPAGAIN .

SPAGAIN
  Refetch the stack pointer. Used after a callback. See the perlcall manpage .

              SPAGAIN;

ST
  Used to access elements on the XSUB's stack.

              SV* ST(int x)

strEQ
  Test two strings to see if they are equal. Returns true or false.

              int strEQ( char *s1, char *s2 )

strGE
  Test two strings to see if the first, `s1`, is greater than or equal to the second, `s2`. Returns true or false.

              int strGE( char *s1, char *s2 )

strGT
  Test two strings to see if the first, `s1`, is greater than the second, `s2`. Returns true or false.

              int strGT( char *s1, char *s2 )

strLE
  Test two strings to see if the first, `s1`, is less than or equal to the second, `s2`. Returns true or false.

              int strLE( char *s1, char *s2 )

strLT
  Test two strings to see if the first, `s1`, is less than the second, `s2`. Returns true or false.

              int strLT( char *s1, char *s2 )

strNE
  Test two strings to see if they are different. Returns true or false.

              int strNE( char *s1, char *s2 )

strnEQ
  Test two strings to see if they are equal. The `len` parameter indicates the number of bytes to compare. Returns true or false.

              int strnEQ( char *s1, char *s2 )

strnNE
  Test two strings to see if they are different. The `len` parameter indicates the number of bytes to compare. Returns true or false.

              int strnNE( char *s1, char *s2, int len )

sv_2mortal
  Marks an SV as mortal. The SV will be destroyed when the current context ends.

              SV*     sv_2mortal _((SV* sv));

sv_bless
  Blesses an SV into a specified package. The SV must be an RV. The package must be designated by its stash (see gv_stashpv() ). The refcount of the SV is unaffected.

              SV*     sv_bless _((SV* sv, HV* stash));

sv_catpv
  Concatenates the string onto the end of the string which is in the SV.

  - void sv_catpv _((SV* sv, char* ptr));

sv_catpvn
  Concatenates the string onto the end of the string which is in the SV. The `len` indicates number of bytes to copy.

  - void sv_catpvn _((SV* sv, char* ptr, STRLEN len));

sv_catsv
  Concatentates the string from SV `ssv` onto the end of the string in SV `dsv`.

  - void sv_catsv _((SV* dsv, SV* ssv));

SvCUR
  Returns the length of the string which is in the SV. See SvLEN .

              int SvCUR (SV* sv)

SvCUR_set
  Set the length of the string which is in the SV. See SvCUR .

              SvCUR_set (SV* sv, int val )

SvEND
  Returns a pointer to the last character in the string which is in the SV. See SvCUR . Access the character as

              *SvEND(sv)

SvGROW
  Expands the character buffer in the SV.

              char * SvGROW( SV* sv, int len )

SvIOK
  Returns a boolean indicating whether the SV contains an integer.

              int SvIOK (SV* SV)

SvIOK_off
  Unsets the IV status of an SV.

              SvIOK_off (SV* sv)

SvIOK_on
  Tells an SV that it is an integer.

              SvIOK_on (SV* sv)

SvIOKp
  Returns a boolean indicating whether the SV contains an integer. Checks the private setting. Use SvIOK .

              int SvIOKp (SV* SV)

sv_isa
  Returns a boolean indicating whether the SV is blessed into the specified class. This does not know how to check for subtype, so it doesn't work in an inheritance relationship.

  - int sv_isa _((SV* sv, char* name));

SvIV
  Returns the integer which is in the SV.

              int SvIV (SV* sv)

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));

SvIVX
  Returns the integer which is stored in the SV.

              int  SvIVX (SV* sv);

SvLEN
  Returns the size of the string buffer in the SV. See SvCUR .

              int SvLEN (SV* sv)

sv_magic
  Adds magic to an SV.

  - void sv_magic _((SV* sv, SV* obj, int how, char* name, I32 namlen));

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));

SvOK
  Returns a boolean indicating whether the value is an SV.

              int SvOK (SV* sv)

sv_newmortal
  Creates a new SV which is mortal. The refcount of the SV is set to 1.

              SV*     sv_newmortal _((void));

sv_no
  This is the `false` SV. See sv_yes . Always refer to this as `&sv_no`.

SvNIOK
  Returns a boolean indicating whether the SV contains a number, integer or double.

              int SvNIOK (SV* SV)

SvNIOK_off
  Unsets the NV/IV status of an SV.

              SvNIOK_off (SV* sv)

SvNIOKp
  Returns a boolean indicating whether the SV contains a number, integer or double. Checks the private setting. Use SvNIOK .

              int SvNIOKp (SV* SV)

SvNOK
  Returns a boolean indicating whether the SV contains a double.

              int SvNOK (SV* SV)

SvNOK_off
  Unsets the NV status of an SV.

              SvNOK_off (SV* sv)

SvNOK_on
  Tells an SV that it is a double.

              SvNOK_on (SV* sv)

SvNOKp
  Returns a boolean indicating whether the SV contains a double. Checks the private setting. Use SvNOK .

              int SvNOKp (SV* SV)

SvNV
  Returns the double which is stored in the SV.

              double SvNV (SV* sv);

SvNVX
  Returns the double which is stored in the SV.

              double SvNVX (SV* sv);

SvPOK
  Returns a boolean indicating whether the SV contains a character string.

              int SvPOK (SV* SV)

SvPOK_off
  Unsets the PV status of an SV.

              SvPOK_off (SV* sv)

SvPOK_on
  Tells an SV that it is a string.

              SvPOK_on (SV* sv)

SvPOKp
  Returns a boolean indicating whether the SV contains a character string. Checks the private setting. Use SvPOK .

              int SvPOKp (SV* SV)

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 `len` is na then Perl will handle the length on its own.

              char * SvPV (SV* sv, int len )

SvPVX
  Returns a pointer to the string in the SV. The SV must contain a string.

              char * SvPVX (SV* sv)

SvREFCNT
  Returns the value of the object's refcount.

              int SvREFCNT (SV* sv);

SvREFCNT_dec
  Decrements the refcount of the given SV.

              void SvREFCNT_dec (SV* sv)

SvREFCNT_inc
  Increments the refcount of the given SV.

              void SvREFCNT_inc (SV* sv)

SvROK
  Tests if the SV is an RV.

              int SvROK (SV* sv)

SvROK_off
  Unsets the RV status of an SV.

              SvROK_off (SV* sv)

SvROK_on
  Tells an SV that it is an RV.

              SvROK_on (SV* sv)

SvRV
  Dereferences an RV to return the SV.

              SV*     SvRV (SV* sv);

sv_setiv
  Copies an integer into the given SV.

  - void sv_setiv _((SV* sv, IV num));

sv_setnv
  Copies a double into the given SV.

  - void sv_setnv _((SV* sv, double num));

sv_setpv
  Copies a string into an SV. The string must be null-terminated.

  - void sv_setpv _((SV* sv, char* ptr));

sv_setpvn
  Copies a string into an SV. The `len` parameter indicates the number of bytes to be copied.

  - void sv_setpvn _((SV* sv, char* ptr, STRLEN len));

sv_setref_iv
  Copies an integer into an SV, optionally blessing the SV. The SV must be an RV. The `classname` argument indicates the package for the blessing. Set `classname` to Nullch to avoid the blessing. The new SV will be returned and will have a refcount of 1.

              SV*     sv_setref_iv _((SV *rv, char *classname, IV iv));

sv_setref_nv
  Copies a double into an SV, optionally blessing the SV. The SV must be an RV. The `classname` argument indicates the package for the blessing. Set `classname` to Nullch to avoid the blessing. The new SV will be returned and will have a refcount of 1.

              SV*     sv_setref_nv _((SV *rv, char *classname, double nv));

sv_setref_pv
  Copies a pointer into an SV, optionally blessing the SV. The SV must be an RV. If the `pv` argument is NULL then sv_undef will be placed into the SV. The `classname` argument indicates the package for the blessing. Set `classname` to Nullch to avoid the blessing. The new SV will be returned and will have a refcount 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 sv_setref_pvn copies the string while this copies the pointer.

sv_setref_pvn
  Copies a string into an SV, optionally blessing the SV. The lenth of the string must be specified with `n`. The SV must be an RV. The `classname` argument indicates the package for the blessing. Set `classname` to Nullch to avoid the blessing. The new SV will be returned and will have a refcount of 1.

              SV*     sv_setref_pvn _((SV *rv, char *classname, char* pv, I32 n));

  Note that sv_setref_pv copies the pointer while this copies the string.

sv_setsv
  Copies the contents of the source SV `ssv` into the destination SV `dsv`.

  - void sv_setsv _((SV* dsv, SV* ssv));

SvSTASH
  Returns the stash of the SV.

              HV * SvSTASH (SV* sv)

SVt_IV
  Integer type flag for scalars. See svtype .

SVt_PV
  Pointer type flag for scalars. See svtype .

SVt_PVAV
  Type flag for arrays. See svtype .

SVt_PVCV
  Type flag for code refs. See svtype .

SVt_PVHV
  Type flag for hashes. See svtype .

SVt_PVMG
  Type flag for blessed scalars. See svtype .

SVt_NV
  Double type flag for scalars. See svtype .

SvTRUE
  Returns a boolean indicating whether Perl would evaluate the SV as true or false, defined or undefined.

              int SvTRUE (SV* sv)

SvTYPE
  Returns the type of the SV. See svtype .

  - svtype SvTYPE (SV* sv)

svtype
  An enum of flags for Perl types. These are found in the file sv.h in the svtype enum. Test these flags with the SvTYPE macro.

SvUPGRADE
  Used to upgrade an SV to a more complex form. See svtype .

sv_undef
  This is the undef SV. Always refer to this as `&sv_undef`.

sv_usepvn
  Tells an SV to use `ptr` to find its string value. Normally the string is stored inside the SV; this allows the SV to use an outside string. The string length, `len`, must be supplied. This function will realloc the memory pointed to by `ptr`, so that pointer should not be freed or used by the programmer after giving it to sv_usepvn.

  - void sv_usepvn _((SV* sv, char* ptr, STRLEN len));

sv_yes
  This is the `true` SV. See sv_no . Always refer to this as `&sv_yes`.

THIS
  Variable which is setup by `xsubpp` to designate the object in a C++ XSUB. This is always the proper type for the C++ object. See CLASS and the perlxs manpage .

toLOWER
  Converts the specified character to lowercase.

              int toLOWER (char c)

toUPPER
  Converts the specified character to uppercase.

              int toUPPER (char c)

warn
  This is the XSUB-writer's interface to Perl's warn function. Use this function the same way you use the C printf function. See croak() .

XPUSHi
  Push an integer onto the stack, extending the stack if necessary. See PUSHi .

              XPUSHi(int d)

XPUSHn
  Push a double onto the stack, extending the stack if necessary. See PUSHn .

              XPUSHn(double d)

XPUSHp
  Push a string onto the stack, extending the stack if necessary. The `len` indicates the length of the string. See PUSHp .

              XPUSHp(char *c, int len)

XPUSHs
  Push an SV onto the stack, extending the stack if necessary. See PUSHs .

              XPUSHs(sv)

XSRETURN
  Return from XSUB, indicating number of items on the stack. This is usually handled by `xsubpp`.

              XSRETURN(x);

XSRETURN_EMPTY
  Return from an XSUB immediately.

              XSRETURN_EMPTY;

XSRETURN_NO
  Return `false` from an XSUB immediately.

              XSRETURN_NO;

XSRETURN_UNDEF
  Return undef from an XSUB immediately.

              XSRETURN_UNDEF;

XSRETURN_YES
  Return `true` from an XSUB immediately.

              XSRETURN_YES;

Zero
  The XSUB-writer's interface to the C `memzero` function. The `d` is the destination, `n` is the number of items, and `t` is the type.

              (void) Zero( d, n, t );

# AUTHOR

Jeff Okamoto <okamoto@corp.hp.com>

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, and Spider Boardman.

API Listing by Dean Roehrich <roehrich@cray.com>.

# DATE

Version 20: 1995/12/14