len);>. It might work with your compiler, but it won't work for everyone.
Break this sort of statement up into separate assignments:
- SV *s;
- STRLEN len;
- char * ptr;
- ptr = SvPV(s, len);
- foo(ptr, len);
+ SV *s;
+ STRLEN len;
+ char * ptr;
+ ptr = SvPV(s, len);
+ foo(ptr, len);
If you want to know if the scalar value is TRUE, you can use:
For example, a tied SV may have a valid underlying value in the IV slot
(so SvIOKp is true), but the data should be accessed via the FETCH
routine rather than directly, so SvIOK is false. Another is when
-numeric conversion has occured and precision has been lost: only the
+numeric conversion has occurred and precision has been lost: only the
private flag is set on 'lossy' values. So when an NV is converted to an
IV with loss, SvIOKp, SvNOKp and SvNOK will be set, while SvIOK wont be.
"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:
+The C<MGVTBL> has five (or sometimes eight) pointers to the following
+routine types:
int (*svt_get)(SV* sv, MAGIC* mg);
int (*svt_set)(SV* sv, MAGIC* mg);
int (*svt_clear)(SV* sv, MAGIC* mg);
int (*svt_free)(SV* sv, MAGIC* mg);
+ int (*svt_copy)(SV *sv, MAGIC* mg, SV *nsv, const char *name, int namlen);
+ int (*svt_dup)(MAGIC *mg, CLONE_PARAMS *param);
+ int (*svt_local)(SV *nsv, MAGIC *mg);
+
+
This MGVTBL structure is set at compile-time in F<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
svt_clear Clear something the SV represents.
svt_free Free any extra storage associated with the SV.
+ svt_copy copy tied variable magic to a tied element
+ svt_dup duplicate a magic structure during thread cloning
+ svt_local copy magic to local value during 'local'
+
For instance, the MGVTBL structure called C<vtbl_sv> (which corresponds
to an C<mg_type> of C<PERL_MAGIC_sv>) contains:
with C<magic_>. NOTE: the magic routines are not considered part of
the Perl API, and may not be exported by the Perl library.
+The last three slots are a recent addition, and for source code
+compatibility they are only checked for if one of the three flags
+MGf_COPY, MGf_DUP or MGf_LOCAL is set in mg_flags. This means that most
+code can continue declaring a vtable as a 5-element value. These three are
+currently used exclusively by the threading code, and are highly subject
+to change.
+
The current kinds of Magic Virtual Tables are:
mg_type
e PERL_MAGIC_envelem vtbl_envelem %ENV hash element
f PERL_MAGIC_fm vtbl_fm Formline ('compiled' format)
g PERL_MAGIC_regex_global vtbl_mglob m//g target / study()ed string
+ H PERL_MAGIC_hints vtbl_sig %^H hash
+ h PERL_MAGIC_hintselem vtbl_hintselem %^H hash element
I PERL_MAGIC_isa vtbl_isa @ISA array
i PERL_MAGIC_isaelem vtbl_isaelem @ISA array element
k PERL_MAGIC_nkeys vtbl_nkeys scalar(keys()) lvalue
y PERL_MAGIC_defelem vtbl_defelem Shadow "foreach" iterator
variable / smart parameter
vivification
- * PERL_MAGIC_glob vtbl_glob GV (typeglob)
# PERL_MAGIC_arylen vtbl_arylen Array length ($#ary)
. PERL_MAGIC_pos vtbl_pos pos() lvalue
- < PERL_MAGIC_backref vtbl_backref ???
+ < PERL_MAGIC_backref vtbl_backref back pointer to a weak ref
~ PERL_MAGIC_ext (none) Available for use by extensions
+ : PERL_MAGIC_symtab (none) hash used as symbol table
+ % PERL_MAGIC_rhash (none) hash used as restricted hash
+ @ PERL_MAGIC_arylen_p vtbl_arylen_p pointer to $#a from @a
+
When an uppercase and lowercase letter both exist in the table, then the
uppercase letter is typically used to represent some kind of composite type
uf.uf_index = 0;
sv_magic(sv, 0, PERL_MAGIC_uvar, (char*)&uf, sizeof(uf));
+Attaching C<PERL_MAGIC_uvar> to arrays is permissible but has no effect.
+
+For hashes there is a specialized hook that gives control over hash
+keys (but not values). This hook calls C<PERL_MAGIC_uvar> 'get' magic
+if the "set" function in the C<ufuncs> structure is NULL. The hook
+is activated whenever the hash is accessed with a key specified as
+an C<SV> through the functions C<hv_store_ent>, C<hv_fetch_ent>,
+C<hv_delete_ent>, and C<hv_exists_ent>. Accessing the key as a string
+through the functions without the C<..._ent> suffix circumvents the
+hook. See L<Hash::Util::Fieldhash/Guts> for a detailed description.
+
Note that because multiple extensions may be using C<PERL_MAGIC_ext>
or C<PERL_MAGIC_uvar> magic, it is important for extensions to take
extra care to avoid conflict. Typically only using the magic on
The following three macros are used to initially allocate memory :
- New(x, pointer, number, type);
- Newc(x, pointer, number, type, cast);
- Newz(x, pointer, number, type);
-
-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.
+ Newx(pointer, number, type);
+ Newxc(pointer, number, type, cast);
+ Newxz(pointer, number, type);
-The second argument C<pointer> should be the name of a variable that will
+The first 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 second and third 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>,
+C<type> is passed to C<sizeof>. The final argument to C<Newxc>, 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>
+Unlike the C<Newx> and C<Newxc> macros, the C<Newxz> macro calls C<memzero>
to zero out all the newly allocated memory.
=head3 Reallocation
support for passing in a "hidden" first argument that represents all three
data structures.
+Two other "encapsulation" macros are the PERL_GLOBAL_STRUCT and
+PERL_GLOBAL_STRUCT_PRIVATE (the latter turns on the former, and the
+former turns on MULTIPLICITY.) The PERL_GLOBAL_STRUCT causes all the
+internal variables of Perl to be wrapped inside a single global struct,
+struct perl_vars, accessible as (globals) &PL_Vars or PL_VarsPtr or
+the function Perl_GetVars(). The PERL_GLOBAL_STRUCT_PRIVATE goes
+one step further, there is still a single struct (allocated in main()
+either from heap or from stack) but there are no global data symbols
+pointing to it. In either case the global struct should be initialised
+as the very first thing in main() using Perl_init_global_struct() and
+correspondingly tear it down after perl_free() using Perl_free_global_struct(),
+please see F<miniperlmain.c> for usage details. You may also need
+to use C<dVAR> in your coding to "declare the global variables"
+when you are using them. dTHX does this for you automatically.
+
+For backward compatibility reasons defining just PERL_GLOBAL_STRUCT
+doesn't actually hide all symbols inside a big global struct: some
+PerlIO_xxx vtables are left visible. The PERL_GLOBAL_STRUCT_PRIVATE
+then hides everything (see how the PERLIO_FUNCS_DECL is used).
+
All this obviously requires a way for the Perl internal functions to be
either subroutines taking some kind of structure as the first
argument, or subroutines taking nothing as the first argument. To
macro with the underscore for functions that take explicit arguments,
or the form without the argument for functions with no explicit arguments.
+If one is compiling Perl with the C<-DPERL_GLOBAL_STRUCT> the C<dVAR>
+definition is needed if the Perl global variables (see F<perlvars.h>
+or F<globvar.sym>) are accessed in the function and C<dTHX> is not
+used (the C<dTHX> includes the C<dVAR> if necessary). One notices
+the need for C<dVAR> only with the said compile-time define, because
+otherwise the Perl global variables are visible as-is.
+
=head2 Should I do anything special if I call perl from multiple threads?
If you create interpreters in one thread and then proceed to call them in
=item A
-This function is a part of the public API.
+This function is a part of the public API. All such functions should also
+have 'd', very few do not.
=item p
-This function has a C<Perl_> prefix; ie, it is defined as C<Perl_av_fetch>
+This function has a C<Perl_> prefix; i.e. it is defined as
+C<Perl_av_fetch>.
=item d
This function has documentation using the C<apidoc> feature which we'll
-look at in a second.
+look at in a second. Some functions have 'd' but not 'A'; docs are good.
=back
=item s
-This is a static function and is defined as C<S_whatever>, and usually
-called within the sources as C<whatever(...)>.
+This is a static function and is defined as C<STATIC S_whatever>, and
+usually called within the sources as C<whatever(...)>.
=item n
-This does not use C<aTHX_> and C<pTHX> to pass interpreter context. (See
+This does not need a interpreter context, so the definition has no
+C<pTHX>, and it follows that callers don't use C<aTHX>. (See
L<perlguts/Background and PERL_IMPLICIT_CONTEXT>.)
=item r
Binary backward compatibility; this function is a macro but also has
a C<Perl_> implementation (which is exported).
+=item others
+
+See the comments at the top of C<embed.fnc> for others.
+
=back
If you edit F<embed.pl> or F<embed.fnc>, you will need to run
=head2 Exception Handling
-There are a couple of macros to do very basic exception handling in
-XS modules. You can use these macros if you call code that may croak,
-but you need to do some cleanup before giving control back to Perl.
-For example:
+There are a couple of macros to do very basic exception handling in XS
+modules. You have to define C<NO_XSLOCKS> before including F<XSUB.h> to
+be able to use these macros:
+
+ #define NO_XSLOCKS
+ #include "XSUB.h"
+
+You can use these macros if you call code that may croak, but you need
+to do some cleanup before giving control back to Perl. For example:
- dXCPT; /* set up neccessary variables */
+ dXCPT; /* set up necessary variables */
XCPT_TRY_START {
code_that_may_croak();
interpreters for other languages in the Perl core, but it also allows
optimizations through the creation of "macro-ops" (ops which perform the
functions of multiple ops which are usually executed together, such as
-C<gvsv, gvsv, add>.)
+C<gvsv, gvsv, add>.)
This feature is implemented as a new op type, C<OP_CUSTOM>. The Perl
core does not "know" anything special about this op type, and so it will
place in the C<PL_custom_op_names> and C<PL_custom_op_descs> hashes.
Forthcoming versions of C<B::Generate> (version 1.0 and above) should
-directly support the creation of custom ops by name; C<Opcodes::Custom>
-will provide functions which make it trivial to "register" custom ops to
-the Perl interpreter.
+directly support the creation of custom ops by name.
=head1 AUTHORS
projects / p5sagit/p5-mst-13.2.git / blobdiff