=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 five routines are:
SV* newSViv(IV);
SV* newSVnv(double);
SV* newSVpv(char*, int);
SV* newSVpvf(const char*, ...);
SV* newSVsv(SV*);
To change the value of an *already-existing* SV, there are six routines:
void sv_setiv(SV*, IV);
void sv_setnv(SV*, double);
void sv_setpv(SV*, char*);
void sv_setpvn(SV*, char*, int)
void sv_setpvf(SV*, const char*, ...);
void sv_setsv(SV*, SV*);
Notice that you can choose to specify the length of the string to be
assigned by using C<sv_setpvn> or C<newSVpv>, or you may allow Perl to
calculate the length by using C<sv_setpv> or by specifying 0 as the second
argument to C<newSVpv>. Be warned, though, that Perl will determine the
string's length by using C<strlen>, which depends on the string terminating
with a NUL character. The arguments of C<sv_setpvf> are processed like
C<sprintf>, and the formatted output becomes the value.
All SVs that will contain strings should, but need not, 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<SvPV> macro, the length of the string returned is placed into the
variable C<len> (this is a macro, so you do I<not> use C<&len>). If you do not
care what the length of the data is, use the global variable C<na>. 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<sv_grow>. Note that C<SvGROW> 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<SvGROW(sv, len + 1)>).
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<SvPOK()> is true.
If you want to append something to the end of string stored in an C<SV*>,
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_catsv(SV*, SV*);
The first function calculates the length of the string to be appended by
using C<strlen>. In the second, you specify the length of the string
yourself. The third function processes its arguments like C<sprintf> and
appends the formatted output. The fourth 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("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<defined>,
you can call:
SvOK(SV*)
The scalar C<undef> value is stored in an SV instance called C<sv_undef>. Its
address can be used whenever an C<SV*> is needed.
There are also the two values C<sv_yes> and C<sv_no>, which contain Boolean
TRUE and FALSE values, respectively. Like C<sv_undef>, their addresses can
be used whenever an C<SV*> is needed.
Do not be fooled into thinking that C<(SV *) 0> is the same as C<&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<&sv_undef> in the first
line and all will be well.
To free an SV that you've created, call C<SvREFCNT_dec(SV*)>. Normally this
call is not necessary (see L<Reference Counts and Mortality>).
=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<Sv*OK> macros. Because a scalar can be both a number and a string,
usually these macros will always return TRUE and calling the C<Sv*V>
macros will do the appropriate conversion of string to integer/double or
integer/double to string.
If you I<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 use the C<Sv*V> 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<num> C<SV*>'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<av_unshift>.
This routine adds C<num> elements at the front of the array with the C<undef>
value. You must then use C<av_store> (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<av_len> function returns the highest index value in array (just
like $#array in Perl). If the array is empty, -1 is returned. The
C<av_fetch> function returns the value at index C<key>, but if C<lval>
is non-zero, then C<av_fetch> will store an undef value at that index.
The C<av_store> function stores the value C<val> at index C<key>.
note that C<av_fetch> and C<av_store> both return C<SV**>'s, not C<SV*>'s
as their return value.
void av_clear(AV*);
void av_undef(AV*);
void av_extend(AV*, I32 key);
The C<av_clear> function deletes all the elements in the AV* array, but
does not actually delete the array itself. The C<av_undef> function will
delete all the elements in the array plus the array itself. The
C<av_extend> function extends the array so that it contains C<key>
elements. If C<key> 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.
=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<klen> parameter is the length of the key being passed in (Note that
you cannot pass 0 in as a value of C<klen> to tell Perl to measure the
length of the key). The C<val> argument contains the SV pointer to the
scalar being stored, and C<hash> is the precomputed hash value (zero if
you want C<hv_store> to calculate it for you). The C<lval> 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<hv_fetch> will return as if the value had already existed.
Remember that C<hv_store> and C<hv_fetch> return C<SV**>'s and not just
C<SV*>. 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<flags> does not include the C<G_DISCARD> flag then C<hv_delete> 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<hv_clear> deletes all the entries in the hash
table but does not actually delete the hash table. The C<hv_undef> 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<SV*>. However,
once you have an C<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("package::varname", FALSE);
This returns NULL if the variable does not exist.
The hash algorithm is defined in the C<PERL_HASH(hash, key, klen)> macro:
i = klen;
hash = 0;
s = key;
while (i--)
hash = hash * 33 + *s++;
=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<SV*> keys, which simplifies writing
of extension code that deals with hash structures. These functions
also allow passing of C<SV*> keys to C<tie> functions without forcing
you to stringify the keys (unlike the previous set of functions).
They also return and accept whole hash entries (C<HE*>), making their
use more efficient (since the hash number for a particular string
doesn't have to be recomputed every time). See L<API LISTING> 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<API LISTING> 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 C<SV*>s:
HeKEY(HE* he)
HeKLEN(HE* he)
=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<thing> argument can be any of an C<SV*>, C<AV*>, or C<HV*>. The
functions are identical except that C<newRV_inc> increments the reference
count of the C<thing>, while C<newRV_noinc> does not. For historical
reasons, C<newRV> is a synonym for C<newRV_inc>.
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<SV*> to either an
C<AV*> or C<HV*>, 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<sv> argument must be a reference. The C<stash> argument specifies
which class the reference will belong to. See
L<Stashes and Globs> 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<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 C<rv>. SV is blessed
if C<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 the pointer value (I<the address, not the string!>) into an SV whose
reference is rv. SV is blessed if C<classname> is non-null.
SV* sv_setref_pv(SV* rv, char* classname, PV iv);
Copies string into an SV whose reference is C<rv>. Set length to 0 to let
Perl calculate the string length. SV is blessed if C<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);
=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<TRUE> argument to enable certain extra features. Those bits are:
GV_ADDMULTI Marks the variable as multiply defined, thus preventing the
"Name <varname> used only once: possible typo" warning.
GV_ADDWARN Issues the warning "Had to create <varname> 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<newRV_inc> 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<newRV_noinc> 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<newRV_inc>, 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<newRV_inc> 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<newRV_noinc> instead of
C<newRV_inc>. 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<perlcall> and L<perlxs> for more details on these macros.
"Mortalization" then is at its simplest a deferred C<SvREFCNT_dec>.
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<SvREFCNT_dec>), 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<SV*>) to the
C<sv_2mortal> or C<sv_mortalcopy> 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
File Handle
Directory Handle
Format
Subroutine
There is a single stash called "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 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<HV*>. The C<create> flag will create a new package if it is set.
The name that C<gv_stash*v> wants is the name of the package whose symbol table
you want. The default package is called C<main>. If you have multiply nested
packages, pass their names to C<gv_stash*v>, 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<SV*>, must be a reference, and the second
argument is a stash. The returned C<SV*> can now be used in the same way
as any other SV.
For more information on references and blessings, consult L<perlref>.
=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<errno>
or its string equivalent from either C<strerror> or C<sys_errlist[]>.
To force multiple data values into an SV, you must do two things: use the
C<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 C<sv_set*v> routine
you called first. This is because every C<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 C<sv_setiv> and C<sv_setpv> had been reversed, then the
macro C<SvPOK_on> would need to be called instead of C<SvIOK_on>.
=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<struct magic>'s, typedef'ed to C<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.
=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<sv> argument is a pointer to the SV that is to acquire a new magical
feature.
If C<sv> is not already magical, Perl uses the C<SvUPGRADE> macro to
set the C<SVt_PVMG> flag for the C<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
overridden, and multiple instances of the same type of magic can be
associated with an SV.
The C<name> and C<namlen> arguments are used to associate a string with
the magic, typically the name of a variable. C<namlen> is stored in the
C<mg_len> field and if C<name> is non-null and C<namlen> >= 0 a malloc'd
copy of the name is stored in C<mg_ptr> field.
The sv_magic function uses C<how> to determine which, if any, predefined
"Magic Virtual Table" should be assigned to the C<mg_virtual> field.
See the "Magic Virtual Table" section below. The C<how> argument is also
stored in the C<mg_type> field.
The C<obj> argument is stored in the C<mg_obj> field of the C<MAGIC>
structure. If it is not the same as the C<sv> argument, the reference
count of the C<obj> object is incremented. If it is the same, or if
the C<how> argument is "#", or if it is a null pointer, then C<obj> is
merely stored, without the reference count being incremented.
There is also a function to add magic to an C<HV>:
void hv_magic(HV *hv, GV *gv, int how);
This simply calls C<sv_magic> and coerces the C<gv> argument into an C<SV>.
To remove the magic from an SV, call the function sv_unmagic:
void sv_unmagic(SV *sv, int type);
The C<type> argument should be equal to the C<how> value when the C<SV>
was initially made magical.
=head2 Magic Virtual Tables
The C<mg_virtual> field in the C<MAGIC> structure is a pointer to a
C<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 C<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 C<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 C<vtbl_sv> (which corresponds
to an C<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 C<magic_get> is called. All
the various routines for the various magical types begin with C<magic_>.
The current kinds of Magic Virtual Tables are:
mg_type MGVTBL Type of magical
------- ------ ----------------------------
\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?
o vtbl_collxfrm Locale transformation
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???
y vtbl_itervar Shadow "foreach" iterator variable
* vtbl_glob GV???
# vtbl_arylen Array Length
. vtbl_pos $. scalar variable
~ None Used by certain extensions
When an uppercase and lowercase letter both exist in the table, then the
uppercase letter is used to represent some kind of composite type (a list
or a hash), and the lowercase letter is used to represent an element of
that composite type.
The '~' magic type is defined specifically for use by extensions and
will not be used by perl itself. Extensions can use ~ magic to 'attach'
private information to variables (typically objects). This is especially
useful because there is no way for normal perl code to corrupt this
private information (unlike using extra elements of a hash object).
Note that because multiple extensions may be using ~ magic it is
important for extensions to take extra care with it. Typically only
using it on objects blessed into the same class as the extension
is sufficient. It may also be appropriate to add an I32 'signature'
at the top of the private data area and check that.
=head2 Finding Magic
MAGIC* mg_find(SV*, int type); /* Finds the magic pointer of that type */
This routine returns a pointer to the C<MAGIC> structure stored in the SV.
If the SV does not have that magical feature, C<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 C<sv> has. If the mg_type
field is an uppercase letter, then the mg_obj is copied to C<nsv>, but
the mg_type field is changed to be the lowercase letter.
=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<ST(n)> macro, which returns
the C<n>'th stack argument. Argument 0 is the first argument passed in the
Perl subroutine call. These arguments are C<SV*>, and can be used anywhere
an C<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 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<sp> is the stack pointer, and C<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 IVs, doubles, strings, and SV pointers respectively:
PUSHi(IV)
PUSHn(double)
PUSHp(char*, I32)
PUSHs(SV*)
And now the Perl program calling C<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. Thus, you
do not need to call C<EXTEND> to extend the stack.
For more information, consult L<perlxs> and L<perlxstut>.
=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<perl_call_sv>. The C<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 C<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 a detailed description of calling conventions from C to Perl,
consult L<perlcall>.
=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<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 (most Perl developers now
use run-time memory checkers), so this argument can be any number.
The second argument C<pointer> should be the name of a variable that will
point to the newly allocated memory.
The third and fourth arguments C<number> and C<type> specify how many of
the specified type of data structure should be allocated. The argument
C<type> is passed to C<sizeof>. The final argument to C<Newc>, C<cast>,
should be used if the C<pointer> argument is different from the C<type>
argument.
Unlike the C<New> and C<Newc> macros, the C<Newz> macro calls C<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 C<Renew> and C<Renewc>
match those of C<New> and C<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 C<source> and C<dest> arguments point to the source and
destination starting points. Perl will move, copy, or zero out C<number>
instances of the size of the C<type> data structure (using the C<sizeof>
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<perlapio>.
=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 (I<target>s) which are (as a corollary)
not constantly freed/created.
Each of the targets is created only once (but see
L<Scratchpads and recursion> 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<target> and puts the I<target> on stack.
The macro to put this target on stack is C<PUSHTARG>, 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 I<target>s 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<SVs_PADMY> set, and
I<target>s have C<SVs_PADTMP> set.
The correspondence between OPs and I<target>s 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<recursion>, and maybe (sometime soon) B<threads>. 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<And> 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 I<target>s on this scratchpad are C<undef>s, 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 reflect 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 + $c> it is different:
some nodes I<optimized away>. As a corollary, though the actual tree
contains more nodes than our simplified example, the execution order
is the same as in our example.
=head2 Examining the tree
If you have your perl compiled for debugging (usually done with C<-D
optimize=-g> on C<Configure> command line), you may examine the
compiled tree by specifying C<-Dx> on the Perl command line. The
output takes several lines per node, and for C<$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<TYPE> 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<gt>> marks, thus it is C<3
4 5 6> (node C<6> is not included into above listing), i.e.,
C<gvsv gvsv add whatever>.
=head2 Compile pass 1: check routines
The tree is created by the I<pseudo-compiler> 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<check routines>. The correspondence between node names
and corresponding check routines is described in F<opcode.pl> (do not
forget to run C<make regen_headers> 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 is 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<ck_*>. They are usually
called from C<new*OP> subroutines (or C<convert>) (which in turn are
called from F<perly.y>).
=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<constant>
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. Aat 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<eval> 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 compilications 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.
=over 8
=item AvFILL
See C<av_len>.
=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<key> 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<key> is the
index. If C<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 C<SV*>.
SV** av_fetch _((AV* ar, I32 key, I32 lval));
=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<&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<key>. The
return value will be null if the operation failed, otherwise it can be
dereferenced to get the original C<SV*>.
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<undef> values onto the beginning of the
array. The array will grow automatically to accommodate the addition.
You must then use C<av_store> to assign values to these new elements.
void av_unshift _((AV* ar, I32 num));
=item CLASS
Variable which is setup by C<xsubpp> to indicate the class name for a C++ XS
constructor. This is always a C<char*>. See C<THIS> and
L<perlxs/"Using XS With C++">.
=item Copy
The XSUB-writer's interface to the C C<memcpy> function. The C<s> is the
source, C<d> is the destination, C<n> is the number of items, and C<t> is
the type. May fail on overlapping copies. See also C<Move>.
(void) Copy( s, d, n, t );
=item croak
This is the XSUB-writer's interface to Perl's C<die> function. Use this
function the same way you use the C C<printf> function. See C<warn>.
=item CvSTASH
Returns the stash of the CV.
HV * CvSTASH( SV* sv )
=item 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<DBsub>.
=item 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<DBsingle>.
The sub name can be found by
SvPV( GvSV( DBsub ), na )
=item 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<DBsingle>.
=item dMARK
Declare a stack marker variable, C<mark>, for the XSUB. See C<MARK> and
C<dORIGMARK>.
=item dORIGMARK
Saves the original stack mark for the XSUB. See C<ORIGMARK>.
=item dowarn
The C variable which corresponds to Perl's $^W warning variable.
=item dSP
Declares a stack pointer variable, C<sp>, for the XSUB. See C<SP>.
=item dXSARGS
Sets up stack and mark pointers for an XSUB, calling dSP and dMARK. This is
usually handled automatically by C<xsubpp>. Declares the C<items> variable
to indicate the number of items on the stack.
=item dXSI32
Sets up the C<ix> variable for an XSUB which has aliases. This is usually
handled automatically by C<xsubpp>.
=item dXSI32
Sets up the C<ix> variable for an XSUB which has aliases. This is usually
handled automatically by C<xsubpp>.
=item ENTER
Opening bracket on a callback. See C<LEAVE> and L<perlcall>.
ENTER;
=item EXTEND
Used to extend the argument stack for an XSUB's return values.
EXTEND( sp, int x );
=item FREETMPS
Closing bracket for temporaries on a callback. See C<SAVETMPS> and
L<perlcall>.
FREETMPS;
=item G_ARRAY
Used to indicate array context. See C<GIMME_V>, C<GIMME> and L<perlcall>.
=item G_DISCARD
Indicates that arguments returned from a callback should be discarded. See
L<perlcall>.
=item G_EVAL
Used to force a Perl C<eval> wrapper around a callback. See L<perlcall>.
=item GIMME
A backward-compatible version of C<GIMME_V> which can only return
C<G_SCALAR> or C<G_ARRAY>; in a void context, it returns C<G_SCALAR>.
=item GIMME_V
The XSUB-writer's equivalent to Perl's C<wantarray>. Returns
C<G_VOID>, C<G_SCALAR> or C<G_ARRAY> for void, scalar or array
context, respectively.
=item G_NOARGS
Indicates that no arguments are being sent to a callback. See L<perlcall>.
=item G_SCALAR
Used to indicate scalar context. See C<GIMME_V>, C<GIMME>, and L<perlcall>.
=item G_VOID
Used to indicate void context. See C<GIMME_V> and L<perlcall>.
=item gv_fetchmeth
Returns the glob with the given C<name> and a defined subroutine or
C<NULL>. The glob lives in the given C<stash>, or in the stashes
accessable via @ISA and @<UNIVERSAL>.
The argument C<level> should be either 0 or -1. If C<level==0>, as a
side-effect creates a glob with the given C<name> in the given
C<stash> 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<gv_fetchmeth> may be a method cache entry,
which is not visible to Perl code. So when calling C<perl_call_sv>,
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<GvCV> 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<stash>. 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<gv_fetchmethod_autoload> 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<gv_fetchmethod> is equivalent to calling C<gv_fetchmethod_autoload> with a
non-zero C<autoload> 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<gv_fetchmeth> with
C<level==0>. C<name> should be writable if contains C<':'> or C<'\''>.
The warning against passing the GV returned by C<gv_fetchmeth> to
C<perl_call_sv> apply equally to these functions.
GV* gv_fetchmethod _((HV* stash, char* name));
GV* gv_fetchmethod_autoload _((HV* stash, char* name,
I32 autoload));
=item gv_stashpv
Returns a pointer to the stash for a specified package. If C<create> is set
then the package will be created if it does not already exist. If C<create>
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<gv_stashpv>.
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<SV*> pointer where a
C<char*> pointer is to be expected. (For information only--not to be used).
=item HeHASH
Returns the computed hash (type C<U32>) stored in the hash entry.
HeHASH(HE* he)
=item HeKEY
Returns the actual pointer stored in the key slot of the hash entry.
The pointer may be either C<char*> or C<SV*>, depending on the value of
C<HeKLEN()>. Can be assigned to. The C<HePV()> or C<HeSVKEY()> macros
are usually preferable for finding the value of a key.
HeKEY(HE* he)
=item HeKLEN
If this is negative, and amounts to C<HEf_SVKEY>, it indicates the entry
holds an C<SV*> key. Otherwise, holds the actual length of the key.
Can be assigned to. The C<HePV()> macro is usually preferable for finding
key lengths.
HeKLEN(HE* he)
=item HePV
Returns the key slot of the hash entry as a C<char*> value, doing any
necessary dereferencing of possibly C<SV*> keys. The length of
the string is placed in C<len> (this is a macro, so do I<not> use
C<&len>). If you do not care about what the length of the key is,
you may use the global variable C<na>. Remember though, that hash
keys in perl are free to contain embedded nulls, so using C<strlen()>
or similar is not a good way to find the length of hash keys.
This is very similar to the C<SvPV()> macro described elsewhere in
this document.
HePV(HE* he, STRLEN len)
=item HeSVKEY
Returns the key as an C<SV*>, or C<Nullsv> if the hash entry
does not contain an C<SV*> key.
HeSVKEY(HE* he)
=item HeSVKEY_force
Returns the key as an C<SV*>. Will create and return a temporary
mortal C<SV*> if the hash entry contains only a C<char*> key.
HeSVKEY_force(HE* he)
=item HeSVKEY_set
Sets the key to a given C<SV*>, taking care to set the appropriate flags
to indicate the presence of an C<SV*> key, and returns the same C<SV*>.
HeSVKEY_set(HE* he, SV* sv)
=item HeVAL
Returns the value slot (type C<SV*>) 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<sv_2mortal>. See C<hv_iternext>
and C<hv_free_ent>.
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<klen> is the length of the key. The
C<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));
=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<flags> value will normally be zero; if set
to G_DISCARD then null will be returned. C<hash> 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<klen> 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<hash>
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<klen> is the length of the key. If C<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 C<SV*>.
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<hash> must be a valid precomputed hash number for the given C<key>, or
0 if you want the function to compute it. IF C<lval> 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<tb> 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.
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<hv_iternext> and C<hv_delayfree_ent>.
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));
=item hv_iterkey
Returns the key from the current position of the hash iterator. See
C<hv_iterinit>.
char* hv_iterkey _((HE* entry, I32* retlen));
=item hv_iterkeysv
Returns the key as an C<SV*> from the current position of the hash
iterator. The return value will always be a mortal copy of the
key. Also see C<hv_iterinit>.
SV* hv_iterkeysv _((HE* entry));
=item hv_iternext
Returns entries from a hash iterator. See C<hv_iterinit>.
HE* hv_iternext _((HV* tb));
=item hv_iternextsv
Performs an C<hv_iternext>, C<hv_iterkey>, and C<hv_iterval> 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<hv_iterkey>.
SV* hv_iterval _((HV* tb, HE* entry));
=item hv_magic
Adds magic to a hash. See C<sv_magic>.
void hv_magic _((HV* hv, GV* gv, int how));
=item HvNAME
Returns the package name of a stash. See C<SvSTASH>, C<CvSTASH>.
char *HvNAME (HV* stash)
=item hv_store
Stores an SV in a hash. The hash key is specified as C<key> and C<klen> is
the length of the key. The C<hash> 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, otherwise it can be dereferenced to get the
original C<SV*>.
SV** hv_store _((HV* tb, char* key, U32 klen, SV* val, U32 hash));
=item hv_store_ent
Stores C<val> in a hash. The hash key is specified as C<key>. The C<hash>
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 entry was stored in a tied hash.
Otherwise the contents of the return value can be accessed using the
C<He???> macros described here.
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<char> is an ascii alphanumeric
character or digit.
int isALNUM (char c)
=item isALPHA
Returns a boolean indicating whether the C C<char> is an ascii alphabetic
character.
int isALPHA (char c)
=item isDIGIT
Returns a boolean indicating whether the C C<char> is an ascii digit.
int isDIGIT (char c)
=item isLOWER
Returns a boolean indicating whether the C C<char> is a lowercase character.
int isLOWER (char c)
=item isSPACE
Returns a boolean indicating whether the C C<char> is whitespace.
int isSPACE (char c)
=item isUPPER
Returns a boolean indicating whether the C C<char> is an uppercase character.
int isUPPER (char c)
=item items
Variable which is setup by C<xsubpp> to indicate the number of items on the
stack. See L<perlxs/"Variable-length Parameter Lists">.
=item ix
Variable which is setup by C<xsubpp> to indicate which of an XSUB's aliases
was used to invoke it. See L<perlxs/"The ALIAS: Keyword">.
=item LEAVE
Closing bracket on a callback. See C<ENTER> and L<perlcall>.
LEAVE;
=item MARK
Stack marker variable for the XSUB. See C<dMARK>.
=item mg_clear
Clear something magical that the SV represents. See C<sv_magic>.
int mg_clear _((SV* sv));
=item mg_copy
Copies the magic from one SV to another. See C<sv_magic>.
int mg_copy _((SV *, SV *, char *, STRLEN));
=item mg_find
Finds the magic pointer for type matching the SV. See C<sv_magic>.
MAGIC* mg_find _((SV* sv, int type));
=item mg_free
Free any magic storage used by the SV. See C<sv_magic>.
int mg_free _((SV* sv));
=item mg_get
Do magic after a value is retrieved from the SV. See C<sv_magic>.
int mg_get _((SV* sv));
=item mg_len
Report on the SV's length. See C<sv_magic>.
U32 mg_len _((SV* sv));
=item mg_magical
Turns on the magical status of an SV. See C<sv_magic>.
void mg_magical _((SV* sv));
=item mg_set
Do magic after a value is assigned to the SV. See C<sv_magic>.
int mg_set _((SV* sv));
=item Move
The XSUB-writer's interface to the C C<memmove> function. The C<s> is the
source, C<d> is the destination, C<n> is the number of items, and C<t> is
the type. Can do overlapping moves. See also C<Copy>.
(void) Move( s, d, n, t );
=item na
A variable which may be used with C<SvPV> to tell Perl to calculate the
string length.
=item New
The XSUB-writer's interface to the C C<malloc> function.
void * New( x, void *ptr, int size, type )
=item Newc
The XSUB-writer's interface to the C C<malloc> function, with cast.
void * Newc( x, void *ptr, int size, type, cast )
=item Newz
The XSUB-writer's interface to the C C<malloc> function. The allocated
memory is zeroed with C<memzero>.
void * Newz( x, void *ptr, int size, type )
=item newAV
Creates a new AV. The reference count is set to 1.
AV* newAV _((void));
=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<not> incremented.
SV* newRV_noinc _((SV* ref));
=item newSV
Creates a new SV. The C<len> parameter indicates the number of bytes of
preallocated string space the SV should have. The reference count for the
new SV is set to 1.
SV* newSV _((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<len> is zero then Perl will compute the length.
SV* newSVpv _((char* s, STRLEN len));
=item newSVrv
Creates a new SV for the RV, C<rv>, to point to. If C<rv> is not an RV then
it will be upgraded to one. If C<classname> 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<xsubpp> to hook up XSUBs as Perl subs.
=item newXSproto
Used by C<xsubpp> to hook up XSUBs as Perl subs. Adds Perl prototypes to
the subs.
=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<dORIGMARK>.
=item perl_alloc
Allocates a new Perl interpreter. See L<perlembed>.
=item perl_call_argv
Performs a callback to the specified Perl sub. See L<perlcall>.
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<perlcall>.
I32 perl_call_method _((char* methname, I32 flags));
=item perl_call_pv
Performs a callback to the specified Perl sub. See L<perlcall>.
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<perlcall>.
I32 perl_call_sv _((SV* sv, I32 flags));
=item perl_construct
Initializes a new Perl interpreter. See L<perlembed>.
=item perl_destruct
Shuts down a Perl interpreter. See L<perlembed>.
=item perl_eval_sv
Tells Perl to C<eval> the string in the SV.
I32 perl_eval_sv _((SV* sv, I32 flags));
=item perl_eval_pv
Tells Perl to C<eval> 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<perlembed>.
=item perl_get_av
Returns the AV of the specified Perl array. If C<create> is set and the
Perl variable does not exist then it will be created. If C<create> 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<create> is set and the Perl
variable does not exist then it will be created. If C<create> 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<create> is set and the Perl
variable does not exist then it will be created. If C<create> 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<create> is set and the
Perl variable does not exist then it will be created. If C<create> 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<perlembed>.
=item perl_require_pv
Tells Perl to C<require> a module.
void perl_require_pv _((char* pv));
=item perl_run
Tells a Perl interpreter to run. See L<perlembed>.
=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<PUTBACK> and L<perlcall>.
PUSHMARK(p)
=item PUSHi
Push an integer onto the stack. The stack must have room for this element.
See C<XPUSHi>.
PUSHi(int d)
=item PUSHn
Push a double onto the stack. The stack must have room for this element.
See C<XPUSHn>.
PUSHn(double d)
=item PUSHp
Push a string onto the stack. The stack must have room for this element.
The C<len> indicates the length of the string. See C<XPUSHp>.
PUSHp(char *c, int len )
=item PUSHs
Push an SV onto the stack. The stack must have room for this element. See
C<XPUSHs>.
PUSHs(sv)
=item PUTBACK
Closing bracket for XSUB arguments. This is usually handled by C<xsubpp>.
See C<PUSHMARK> and L<perlcall> for other uses.
PUTBACK;
=item Renew
The XSUB-writer's interface to the C C<realloc> function.
void * Renew( void *ptr, int size, type )
=item Renewc
The XSUB-writer's interface to the C C<realloc> function, with cast.
void * Renewc( void *ptr, int size, type, cast )
=item RETVAL
Variable which is setup by C<xsubpp> to hold the return value for an XSUB.
This is always the proper type for the XSUB.
See L<perlxs/"The RETVAL Variable">.
=item safefree
The XSUB-writer's interface to the C C<free> function.
=item safemalloc
The XSUB-writer's interface to the C C<malloc> function.
=item saferealloc
The XSUB-writer's interface to the C C<realloc> 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<len> 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<FREETMPS> and
L<perlcall>.
SAVETMPS;
=item SP
Stack pointer. This is usually handled by C<xsubpp>. See C<dSP> and
C<SPAGAIN>.
=item SPAGAIN
Refetch the stack pointer. Used after a callback. See L<perlcall>.
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<s1>, is greater than or equal to the
second, C<s2>. Returns true or false.
int strGE( char *s1, char *s2 )
=item strGT
Test two strings to see if the first, C<s1>, is greater than the second,
C<s2>. Returns true or false.
int strGT( char *s1, char *s2 )
=item strLE
Test two strings to see if the first, C<s1>, is less than or equal to the
second, C<s2>. Returns true or false.
int strLE( char *s1, char *s2 )
=item strLT
Test two strings to see if the first, C<s1>, is less than the second,
C<s2>. 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<len> 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<len> 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<gv_stashpv()>). 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.
void sv_catpv _((SV* sv, char* ptr));
=item sv_catpvn
Concatenates the string onto the end of the string which is in the SV. The
C<len> indicates number of bytes to copy.
void sv_catpvn _((SV* sv, char* ptr, STRLEN len));
=item sv_catpvf
Processes its arguments like C<sprintf> and appends the formatted output
to an SV.
void sv_catpvf _((SV* sv, const char* pat, ...));
=item sv_catsv
Concatenates the string from SV C<ssv> onto the end of the string in SV
C<dsv>.
void sv_catsv _((SV* dsv, SV* ssv));
=item sv_cmp
Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
string in C<sv1> is less than, equal to, or greater than the string in
C<sv2>.
I32 sv_cmp _((SV* sv1, SV* sv2));
=item sv_cmp
Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
string in C<sv1> is less than, equal to, or greater than the string in
C<sv2>.
I32 sv_cmp _((SV* sv1, SV* sv2));
=item SvCUR
Returns the length of the string which is in the SV. See C<SvLEN>.
int SvCUR (SV* sv)
=item SvCUR_set
Set the length of the string which is in the SV. See C<SvCUR>.
SvCUR_set (SV* sv, int val )
=item sv_dec
Auto-decrement of the value in the SV.
void sv_dec _((SV* sv));
=item sv_dec
Auto-decrement of the value in the SV.
void sv_dec _((SV* sv));
=item SvEND
Returns a pointer to the last character in the string which is in the SV.
See C<SvCUR>. Access the character as
*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 SvGROW
Expands the character buffer in the SV. Calls C<sv_grow> 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<sv_unref> and will
upgrade the SV to C<SVt_PV>. Returns a pointer to the character buffer.
Use C<SvGROW>.
=item sv_inc
Auto-increment of the value in the SV.
void sv_inc _((SV* sv));
=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.
SvIOK_off (SV* sv)
=item SvIOK_on
Tells an SV that it is an integer.
SvIOK_on (SV* sv)
=item SvIOK_only
Tells an SV that it is an integer and disables all other OK bits.
SvIOK_on (SV* sv)
=item SvIOK_only
Tells an SV that it is an integer and disables all other OK bits.
SvIOK_on (SV* sv)
=item SvIOKp
Returns a boolean indicating whether the SV contains an integer. Checks the
B<private> setting. Use C<SvIOK>.
int SvIOKp (SV* SV)
=item 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));
=item SvIV
Returns the integer which is in the SV.
int SvIV (SV* sv)
=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 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<SvCUR>.
int SvLEN (SV* sv)
=item sv_len
Returns the length of the string in the SV. Use C<SvCUR>.
STRLEN sv_len _((SV* sv));
=item sv_len
Returns the length of the string in the SV. Use C<SvCUR>.
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 SvOK
Returns a boolean indicating whether the value is an SV.
int SvOK (SV* sv)
=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 sv_no
This is the C<false> SV. See C<sv_yes>. Always refer to this as C<&sv_no>.
=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.
SvNIOK_off (SV* sv)
=item SvNIOKp
Returns a boolean indicating whether the SV contains a number, integer or
double. Checks the B<private> setting. Use C<SvNIOK>.
int SvNIOKp (SV* SV)
=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.
SvNOK_off (SV* sv)
=item SvNOK_on
Tells an SV that it is a double.
SvNOK_on (SV* sv)
=item SvNOK_only
Tells an SV that it is a double and disables all other OK bits.
SvNOK_on (SV* sv)
=item SvNOK_only
Tells an SV that it is a double and disables all other OK bits.
SvNOK_on (SV* sv)
=item SvNOKp
Returns a boolean indicating whether the SV contains a double. Checks the
B<private> setting. Use C<SvNOK>.
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 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.
SvPOK_off (SV* sv)
=item SvPOK_on
Tells an SV that it is a string.
SvPOK_on (SV* sv)
=item SvPOK_only
Tells an SV that it is a string and disables all other OK bits.
SvPOK_on (SV* sv)
=item SvPOK_only
Tells an SV that it is a string and disables all other OK bits.
SvPOK_on (SV* sv)
=item SvPOKp
Returns a boolean indicating whether the SV contains a character string.
Checks the B<private> setting. Use C<SvPOK>.
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<len> is C<na> then Perl will
handle the length on its own.
char * SvPV (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.
SvROK_off (SV* sv)
=item SvROK_on
Tells an SV that it is an RV.
SvROK_on (SV* sv)
=item SvRV
Dereferences an RV to return the SV.
SV* SvRV (SV* sv);
=item sv_setiv
Copies an integer into the given SV.
void sv_setiv _((SV* sv, IV num));
=item sv_setnv
Copies a double into the given SV.
void sv_setnv _((SV* sv, double num));
=item sv_setpv
Copies a string into an SV. The string must be null-terminated.
void sv_setpv _((SV* sv, char* ptr));
=item sv_setpvn
Copies a string into an SV. The C<len> parameter indicates the number of
bytes to be copied.
void sv_setpvn _((SV* sv, char* ptr, STRLEN len));
=item sv_setpvf
Processes its arguments like C<sprintf> and sets an SV to the formatted
output.
void sv_setpvf _((SV* sv, const char* pat, ...));
=item sv_setref_iv
Copies an integer into a new SV, optionally blessing the SV. The C<rv>
argument will be upgraded to an RV. That RV will be modified to point to
the new SV. The C<classname> argument indicates the package for the
blessing. Set C<classname> to C<Nullch> 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<rv>
argument will be upgraded to an RV. That RV will be modified to point to
the new SV. The C<classname> argument indicates the package for the
blessing. Set C<classname> to C<Nullch> 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<rv>
argument will be upgraded to an RV. That RV will be modified to point to
the new SV. If the C<pv> argument is NULL then C<sv_undef> will be placed
into the SV. The C<classname> argument indicates the package for the
blessing. Set C<classname> to C<Nullch> 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<sv_setref_pvn> 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<n>. The C<rv> argument will be upgraded to
an RV. That RV will be modified to point to the new SV. The C<classname>
argument indicates the package for the blessing. Set C<classname> to
C<Nullch> 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<sv_setref_pv> copies the pointer while this copies the string.
=item sv_setsv
Copies the contents of the source SV C<ssv> into the destination SV C<dsv>.
The source SV may be destroyed if it is mortal.
void sv_setsv _((SV* dsv, SV* ssv));
=item SvSTASH
Returns the stash of the SV.
HV * SvSTASH (SV* sv)
=item SVt_IV
Integer type flag for scalars. See C<svtype>.
=item SVt_PV
Pointer type flag for scalars. See C<svtype>.
=item SVt_PVAV
Type flag for arrays. See C<svtype>.
=item SVt_PVCV
Type flag for code refs. See C<svtype>.
=item SVt_PVHV
Type flag for hashes. See C<svtype>.
=item SVt_PVMG
Type flag for blessed scalars. See C<svtype>.
=item SVt_NV
Double type flag for scalars. See C<svtype>.
=item SvTRUE
Returns a boolean indicating whether Perl would evaluate the SV as true or
false, defined or undefined.
int SvTRUE (SV* sv)
=item SvTYPE
Returns the type of the SV. See C<svtype>.
svtype SvTYPE (SV* sv)
=item svtype
An enum of flags for Perl types. These are found in the file B<sv.h> in the
C<svtype> enum. Test these flags with the C<SvTYPE> macro.
=item SvUPGRADE
Used to upgrade an SV to a more complex form. Uses C<sv_upgrade> to perform
the upgrade if necessary. See C<svtype>.
bool SvUPGRADE _((SV* sv, svtype mt));
=item sv_upgrade
Upgrade an SV to a more complex form. Use C<SvUPGRADE>. See C<svtype>.
=item sv_undef
This is the C<undef> SV. Always refer to this as C<&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<newSVrv>. See C<SvROK_off>.
void sv_unref _((SV* sv));
=item sv_usepvn
Tells an SV to use C<ptr> 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<ptr> should point to memory that was allocated by C<malloc>. The
string length, C<len>, must be supplied. This function will realloc the
memory pointed to by C<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));
=item sv_yes
This is the C<true> SV. See C<sv_no>. Always refer to this as C<&sv_yes>.
=item THIS
Variable which is setup by C<xsubpp> to designate the object in a C++ XSUB.
This is always the proper type for the C++ object. See C<CLASS> and
L<perlxs/"Using XS With C++">.
=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<warn> function. Use this
function the same way you use the C C<printf> function. See C<croak()>.
=item XPUSHi
Push an integer onto the stack, extending the stack if necessary. See
C<PUSHi>.
XPUSHi(int d)
=item XPUSHn
Push a double onto the stack, extending the stack if necessary. See
C<PUSHn>.
XPUSHn(double d)
=item XPUSHp
Push a string onto the stack, extending the stack if necessary. The C<len>
indicates the length of the string. See C<PUSHp>.
XPUSHp(char *c, int len)
=item XPUSHs
Push an SV onto the stack, extending the stack if necessary. See C<PUSHs>.
XPUSHs(sv)
=item XS
Macro to declare an XSUB and its C parameter list. This is handled by
C<xsubpp>.
=item XSRETURN
Return from XSUB, indicating number of items on the stack. This is usually
handled by C<xsubpp>.
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<XST_mIV>.
XSRETURN_IV(IV v);
=item XSRETURN_NO
Return C<&sv_no> from an XSUB immediately. Uses C<XST_mNO>.
XSRETURN_NO;
=item XSRETURN_NV
Return an double from an XSUB immediately. Uses C<XST_mNV>.
XSRETURN_NV(NV v);
=item XSRETURN_PV
Return a copy of a string from an XSUB immediately. Uses C<XST_mPV>.
XSRETURN_PV(char *v);
=item XSRETURN_UNDEF
Return C<&sv_undef> from an XSUB immediately. Uses C<XST_mUNDEF>.
XSRETURN_UNDEF;
=item XSRETURN_YES
Return C<&sv_yes> from an XSUB immediately. Uses C<XST_mYES>.
XSRETURN_YES;
=item XST_mIV
Place an integer into the specified position C<i> 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<i> on the stack. The value is
stored in a new mortal SV.
XST_mNV( int i, NV v );
=item XST_mNO
Place C<&sv_no> into the specified position C<i> on the stack.
XST_mNO( int i );
=item XST_mPV
Place a copy of a string into the specified position C<i> on the stack. The
value is stored in a new mortal SV.
XST_mPV( int i, char *v );
=item XST_mUNDEF
Place C<&sv_undef> into the specified position C<i> on the stack.
XST_mUNDEF( int i );
=item XST_mYES
Place C<&sv_yes> into the specified position C<i> on the stack.
XST_mYES( int i );
=item XS_VERSION
The version identifier for an XS module. This is usually handled
automatically by C<ExtUtils::MakeMaker>. See C<XS_VERSION_BOOTCHECK>.
=item XS_VERSION_BOOTCHECK
Macro to verify that a PM module's $VERSION variable matches the XS module's
C<XS_VERSION> variable. This is usually handled automatically by
C<xsubpp>. See L<perlxs/"The VERSIONCHECK: Keyword">.
=item Zero
The XSUB-writer's interface to the C C<memzero> function. The C<d> is the
destination, C<n> is the number of items, and C<t> is the type.
(void) Zero( d, n, t );
=back
=head1 EDITOR
Jeff Okamoto <F<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, Spider Boardman, and Ulrich Pfeifer.
API Listing by Dean Roehrich <F<roehrich@cray.com>>.
=head1 DATE
Version 31.7: 1997/5/1