Perl executable. It is far from complete and probably contains many errors.
Please refer any questions or comments to the author below.
-=head1 Datatypes
+=head1 Variables
+
+=head2 Datatypes
Perl has three typedefs that handle Perl's three main data types:
=head2 What is an "IV"?
-Perl uses a special typedef IV which is large enough to hold either an
-integer or a pointer.
+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
+=head2 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,
string's length by using C<strlen>, which depends on the string terminating
with a NUL character.
+All SV's 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*)
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 not be terminated by a NUL.
+NUL's and might not be terminated by a NUL.
-If you want to know simply if the scalar value is TRUE, you can use:
+If you want to know if the scalar value is TRUE, you can use:
SvTRUE(SV*)
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.
+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.
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);
+ SV* perl_get_sv("package::varname", FALSE);
This returns NULL if the variable does not exist.
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 plain weird results. Change the zero to C<&sv_undef> in
-the first line and all will be well.
+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 the section on L<Mortality>.
+call is not necessary (see the section on L<Reference Counts and Mortality>).
=head2 What's Really Stored in an 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 just to use the C<Sv*V> macros.
+In general, though, it's best to use the C<Sv*V> macros.
-=head2 Working with AVs
+=head2 Working with AV's
-There are two ways to create and load an AV. The first method creates just
-an empty AV:
+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:
+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 C<num> C<SV*>s. Once the
-AV has been created, the SVs can be destroyed, if so desired.
+The second argument points to an array containing C<num> C<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 AVs:
+Once the AV has been created, the following operations are possible on AV's:
void av_push(AV*, SV*);
SV* av_pop(AV*);
Here are some other functions:
- I32 av_len(AV*); /* Returns highest index value in array */
-
+ I32 av_len(AV*);
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 C<av_fetch> and C<av_store> return C<SV**>s, not C<SV*>s.
+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*);
- /* 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 */
+
+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("varname", FALSE);
+ AV* perl_get_av("package::varname", FALSE);
This returns NULL if the variable does not exist.
-=head2 Working with HVs
+=head2 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 HVs:
+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 C<klen> parameter is the length of the key being passed in. The C<val>
-argument contains the SV pointer to the scalar being stored, and C<hash> is
-the pre-computed 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.
+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 pre-computed 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.
+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*);
- /* Clears all entries in hash table */
void hv_undef(HV*);
- /* Undefines the hash table */
+
+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
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);
+ HV* perl_get_hv("package::varname", FALSE);
This returns NULL if the variable does not exist.
-The hash algorithm, for those who are interested, is:
+The hash algorithm is defined in the C<PERL_HASH(hash, key, klen)> macro:
i = klen;
hash = 0;
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 the following command:
+To create a reference, use either of the following functions:
+
+ SV* newRV_inc((SV*) thing);
+ SV* newRV_noinc((SV*) thing);
- SV* newRV((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>.
-The C<thing> argument can be any of an C<SV*>, C<AV*>, or C<HV*>. Once
-you have a reference, you can use the following macro to dereference the
-reference:
+Once you have a reference, you can use the following macro to dereference
+the reference:
SvRV(SV*)
SvROK(SV*)
-To discover what the reference actually refers to, you must use the following
-macro and then check the value returned.
+To discover what type of value the reference refers to, use the following
+macro and then check the return value.
SvTYPE(SvRV(SV*))
SVt_IV Scalar
SVt_NV Scalar
SVt_PV Scalar
+ SVt_RV Scalar
SVt_PVAV Array
SVt_PVHV Hash
SVt_PVCV Code
- SVt_PVMG Blessed Scalar
+ 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
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 the section on L<Stashes>
-for information on converting class names into stashes.
+which class the reference will belong to. See the section on
+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 classname is non-null, the SV is blessed into the specified class.
-SV is returned.
+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 rv. SV is blessed
-if classname is non-null.
+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 pointer (I<not a string!>) into an SV whose reference is rv.
-SV is blessed if classname is non-null.
+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 rv.
-Set length to 0 to let Perl calculate the string length.
-SV is blessed if classname is non-null.
+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);
-=head1 Creating New Variables
+=head2 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.
+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("varname", TRUE);
- AV* perl_get_av("varname", TRUE);
- HV* perl_get_hv("varname", TRUE);
+ 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 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
- "Identifier <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 exist already and want to propagate
- this warning back to the user.
-
-If the C<varname> argument does not contain a package specifier, it is
-created in the current package.
-
-=head1 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>.
-
-=head1 Localizing Changes
-
-Perl has a very handy construction
-
- {
- local $var = 2;
- ...
- }
-
-This construction is I<approximately> equivalent to
-
- {
- my $oldvar = $var;
- $var = 2;
- ...
- $var = $oldvar;
- }
-
-The biggest difference is that the first construction would would
-reinstate the initial value of $var, irrespective of how control exits
-the block: C<goto>, C<return>, C<die>/C<eval> etc. It is a little bit
-more efficient as well.
-
-There is a way to achieve a similar task from C via Perl API: create a
-I<pseudo-block>, and arrange for some changes to be automatically
-undone at the end of it, either explicit, or via a non-local exit (via
-die()). A I<block>-like construct is created by a pair of
-C<ENTER>/C<LEAVE> macros (see L<perlcall/EXAMPLE/"Returning a
-Scalar">). Such a construct may be created specially for some
-important localized task, or an existing one (like boundaries of
-enclosing Perl subroutine/block, or an existing pair for freeing TMPs)
-may be used. (In the second case the overhead of additional
-localization must be almost negligible.) Note that any XSUB is
-automatically enclosed in an C<ENTER>/C<LEAVE> pair.
-
-Inside such a I<pseudo-block> the following service is available:
-
-=over
-
-=item C<SAVEINT(int i)>
-
-=item C<SAVEIV(IV i)>
+There are additional macros whose values may be bitwise OR'ed with the
+C<TRUE> argument to enable certain extra features. Those bits are:
-=item C<SAVEI16(I16 i)>
+ GV_ADDMULTI Marks the variable as multiply defined, thus preventing the
+ "Indentifier <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.
-=item C<SAVEI32(I32 i)>
+If you do not specify a package name, the variable is created in the current
+package.
-=item C<SAVELONG(long i)>
-
-These macros arrange things to restore the value of integer variable
-C<i> at the end of enclosing I<pseudo-block>.
-
-=item C<SAVESPTR(p)>
-
-=item C<SAVEPPTR(s)>
-
-These macros arrange things to restore the value of pointers C<s> and
-C<p>. C<p> must be a pointer of a type which survives conversion to
-C<SV*> and back, C<s> should be able to survive conversion to C<char*>
-and back.
-
-=item C<SAVEFREESV(SV *sv)>
-
-The reference count of C<sv> would be decremented at the end of
-I<pseudo-block>. This is similar to C<sv_2mortal>, which should (?) be
-used instead.
-
-=item C<SAVEFREEOP(OP *op)>
-
-The C<OP *> is op_free()ed at the end of I<pseudo-block>.
-
-=item C<SAVEFREEPV(p)>
-
-The chunk of memory which is pointed to by C<p> is Safefree()ed at the
-end of I<pseudo-block>.
-
-=item C<SAVECLEARSV(SV *sv)>
-
-Clears a slot in the current scratchpad which corresponds to C<sv> at
-the end of I<pseudo-block>.
-
-=item C<SAVEDELETE(HV *hv, char *key, I32 length)>
-
-The key C<key> of C<hv> is deleted at the end of I<pseudo-block>. The
-string pointed to by C<key> is Safefree()ed. If one has a I<key> in
-short-lived storage, the corresponding string may be reallocated like
-this:
-
- SAVEDELETE(defstash, savepv(tmpbuf), strlen(tmpbuf));
-
-=item C<SAVEDESTRUCTOR(f,p)>
-
-At the end of I<pseudo-block> the function C<f> is called with the
-only argument (of type C<void*>) C<p>.
-
-=item C<SAVESTACK_POS()>
-
-The current offset on the Perl internal stack (cf. C<SP>) is restored
-at the end of I<pseudo-block>.
-
-=back
-
-The following API list contains functions, thus one needs to
-provide pointers to the modifiable data explicitly (either C pointers,
-or Perlish C<GV *>s):
-
-=over
-
-=item C<SV* save_scalar(GV *gv)>
-
-Equivalent to Perl code C<local $gv>.
-
-=item C<AV* save_ary(GV *gv)>
-
-=item C<HV* save_hash(GV *gv)>
-
-Similar to C<save_scalar>, but localize C<@gv> and C<%gv>.
-
-=item C<void save_item(SV *item)>
-
-Duplicates the current value of C<SV>, on the exit from the current
-C<ENTER>/C<LEAVE> I<pseudo-block> will restore the value of C<SV>
-using the stored value.
-
-=item C<void save_list(SV **sarg, I32 maxsarg)>
-
-A variant of C<save_item> which takes multiple arguments via an array
-C<sarg> of C<SV*> of length C<maxsarg>.
-
-=item C<SV* save_svref(SV **sptr)>
-
-Similar to C<save_scalar>, but will reinstate a C<SV *>.
-
-=item C<void save_aptr(AV **aptr)>
-
-=item C<void save_hptr(HV **hptr)>
-
-Similar to C<save_svref>, but localize C<AV *> and C<HV *>.
-
-=item C<void save_nogv(GV *gv)>
-
-Will postpone destruction of a I<stub> glob.
-
-=back
-
-=head1 Mortality
+=head2 Reference Counts and Mortality
Perl uses an reference count-driven garbage collection mechanism. SV's,
AV's, or HV's (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 they will be destroyed and their memory made available for reuse.
+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. At the internal level, however, reference counts can be
+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);
- void SvREFCNT_inc(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> function, as you should recall,
-creates a reference to the specified argument. As a side effect, it
-increments the argument's reference count, which is ok in most
-circumstances. But imagine you want to return a reference from an XS
-function. You create a new SV which initially has a reference count
-of 1. Then you call C<newRV>, passing the just-created SV. This returns
-the reference as a new SV, but the reference count of the SV you passed
-to C<newRV> has been incremented to 2. Now you return the reference 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 1
-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 call C<SvREFCNT_dec> on the SV after
-C<newRV> has returned. Then, if and when the reference is destroyed,
-the reference count of the SV will go to 0 and also be destroyed, stopping
-any memory leak.
-
-There are some convenience functions available that can help with this
-process. 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 the "current context" is left.
-Generally the "current context" means a single Perl statement, such as
-a call to an XSUB function.
+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 xV's. 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 xV's 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
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. Doing the latter can
-cause a variable to become invalid prematurely.
+or if you make a variable mortal multiple times.
To create a mortal variable, use the functions:
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 (possibly
-destroying it in the process).
-
-The mortal routines are not for just SVs -- AVs and HVs can be made mortal
-by passing their address (and casting them to C<SV*>) to the C<sv_2mortal> or
-C<sv_mortalcopy> routines.
+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.
-I<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 I<should>
-be mortal.
+The mortal routines are not just for SV's -- AV's and HV's 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
-=head1 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:
+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
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 C<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.
+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:
char* HvNAME(HV* stash);
-If you need to return a blessed value to your Perl script, you can use the
-following function:
+If you need to bless or re-bless an object you can use the following
+function:
SV* sv_bless(SV*, HV* stash)
For more information on references and blessings, consult L<perlref>.
-=head1 Magic
+=head2 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 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>.
+linked list of C<struct magic>'s, typedef'ed to C<MAGIC>.
struct magic {
MAGIC* mg_moremagic;
The current kinds of Magic Virtual Tables are:
- mg_type MGVTBL Type of magic
- ------- ------ -------------------
+ mg_type MGVTBL Type of magical
+ ------- ------ ----------------------------
\0 vtbl_sv Regexp???
A vtbl_amagic Operator Overloading
a vtbl_amagicelem Operator Overloading
i vtbl_isaelem @ISA array element
L 0 (but sets RMAGICAL) Perl Module/Debugger???
l vtbl_dbline Debugger?
- o vtbl_collxfrm Locale Collation
+ 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
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
- ~ Reserved for extensions, but multiple extensions may clash
+ ~ None Used by certain extensions
-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
+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 */
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 upper-case letter, then the mg_obj is copied to C<nsv>, but
-the mg_type field is changed to be the lower-case letter.
+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 Double-Typed SVs
+=head1 Subroutines
-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.
+=head2 XSUBs and the Argument Stack
-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[]>.
+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.
-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:
+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.
- SvIOK_on
- SvNOK_on
- SvPOK_on
- SvROK_on
+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.
-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.
+To handle this situation, the PPCODE directive is used and the stack is
+extended using the macro:
-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:
+ EXTEND(sp, num);
- extern int dberror;
- extern char *dberror_list;
+where C<sp> is the stack pointer, and C<num> is the number of elements the
+stack should be extended by.
- SV* sv = perl_get_sv("dberror", TRUE);
- sv_setiv(sv, (IV) dberror);
- sv_setpv(sv, dberror_list[dberror]);
- SvIOK_on(sv);
+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:
-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>.
+ PUSHi(IV)
+ PUSHn(double)
+ PUSHp(char*, I32)
+ PUSHs(SV*)
-=head1 Calling Perl Routines from within C Programs
+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:
XPUSH*()
POP*()
-For more information, consult L<perlcall>.
+For a detailed description of calling conventions from C to Perl,
+consult L<perlcall>.
-=head1 Memory Allocation
+=head2 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 to
-satisfy allocation requests more quickly.
-However, on some platforms, it may cause spurious malloc or free errors.
+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 allocate memory initially. 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 (Larry has switched to using a run-time memory checker),
-so this argument can be any number.
+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 second argument C<pointer> 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>,
instances of the size of the C<type> data structure (using the C<sizeof>
function).
-=head1 Scratchpads
+=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
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
+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.
=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
+The question remains on when the SV's 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.
-Scratchpad keeps SVs which are lexicals for the current unit and are
+A scratchpad keeps SV's 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
+The correspondence between OP's and I<target>s is not 1-to-1. Different
+OP's 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 recursions
+=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
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
+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
Used to indicate scalar context. See C<GIMME> 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
+
+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 corresponing variable
+$AUTOLOAD is already setup.
+
+Note that if you want to keep this 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.
+
+This function grants C<"SUPER"> token as a prefix of the method name.
+
+Has 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 C<gv_fetchmethod>.
+
+ GV* gv_fetchmethod _((HV* stash, char* name));
+
=item gv_stashpv
Returns a pointer to the stash for a specified package. If C<create> is set
Return the SV from the GV.
-=item he_free
+=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)
-Releases a hash entry from an iterator. See C<hv_iternext>.
+=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
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
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 pre-computed
+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
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 pre-computed 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
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 pre-computed 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.
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>.
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 pre-computed 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.
=item isALNUM
Returns a boolean indicating whether the C C<char> is an ascii alphanumeric
-character.
+character or digit.
int isALNUM (char c)
HV* newHV _((void));
-=item newRV
+=item newRV_inc
Creates an RV wrapper for an SV. The reference count for the original SV is
incremented.
- SV* newRV _((SV* ref));
+ 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
-pre-allocated string space the SV should have. The reference count for the new SV
-is set to 1.
+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.
+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.
+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.
+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 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.
+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_inc
-Auto increment of the value in the SV.
+Auto-increment of the value in the SV.
void sv_inc _((SV* sv));
=item sv_mortalcopy
Creates a new SV which is a copy of the original SV. The new SV is marked
-as mortal. The old SV may become invalid if it was marked as a temporary.
+as mortal.
SV* sv_mortalcopy _((SV* oldsv));
=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 or temporary.
+The source SV may be destroyed if it is mortal.
void sv_setsv _((SV* dsv, SV* ssv));
-=item SvSetSV
-
-A wrapper around C<sv_setsv>. Safe even if C<dst==ssv>.
-
=item SvSTASH
Returns the stash of the SV.
=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>.
+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));
=back
-=head1 AUTHOR
+=head1 EDITOR
-Jeff Okamoto <okamoto@corp.hp.com>
+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 <roehrich@cray.com>.
+API Listing by Dean Roehrich <F<roehrich@cray.com>>.
=head1 DATE
-Version 23.1: 1996/10/19
+Version 31.3: 1997/3/14
projects / p5sagit/p5-mst-13.2.git / blobdiff