From: Rafael Garcia-Suarez Date: Wed, 18 Jun 2003 20:47:47 +0000 (+0000) Subject: A bunch of minor changes to perlguts.pod. X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=commitdiff_plain;h=06f6df1768f7810ef4b2d5d7821dcccb9c7bf9e4;p=p5sagit%2Fp5-mst-13.2.git A bunch of minor changes to perlguts.pod. p4raw-id: //depot/perl@19815 --- diff --git a/pod/perlguts.pod b/pod/perlguts.pod index 79354c2..9a411e1 100644 --- a/pod/perlguts.pod +++ b/pod/perlguts.pod @@ -5,7 +5,7 @@ perlguts - Introduction to the Perl API =head1 DESCRIPTION This document attempts to describe how to use the Perl API, as well as -containing some info on the basic workings of the Perl core. It is far +to provide some info on the basic workings of the Perl core. It is far from complete and probably contains many errors. Please refer any questions or comments to the author below. @@ -43,26 +43,31 @@ The seven routines are: SV* newSViv(IV); SV* newSVuv(UV); SV* newSVnv(double); - SV* newSVpv(const char*, int); - SV* newSVpvn(const char*, int); + SV* newSVpv(const char*, STRLEN); + SV* newSVpvn(const char*, STRLEN); SV* newSVpvf(const char*, ...); SV* newSVsv(SV*); -If you require more complex initialisation you can create an empty SV with -newSV(len). If C is 0 an empty SV of type NULL is returned, else an -SV of type PV is returned with len + 1 (for the NUL) bytes of storage -allocated, accessible via SvPVX. In both cases the SV has value undef. +C is an integer type (Size_t, usually defined as size_t in +F) guaranteed to be large enough to represent the size of +any string that perl can handle. + +In the unlikely case of a SV requiring more complex initialisation, you +can create an empty SV with newSV(len). If C is 0 an empty SV of +type NULL is returned, else an SV of type PV is returned with len + 1 (for +the NUL) bytes of storage allocated, accessible via SvPVX. In both cases +the SV has value undef. - SV* newSV(0); /* no storage allocated */ - SV* newSV(10); /* 10 (+1) bytes of uninitialised storage allocated */ + SV *sv = newSV(0); /* no storage allocated */ + SV *sv = newSV(10); /* 10 (+1) bytes of uninitialised storage allocated */ -To change the value of an *already-existing* SV, there are eight routines: +To change the value of an I SV, there are eight routines: void sv_setiv(SV*, IV); void sv_setuv(SV*, UV); void sv_setnv(SV*, double); void sv_setpv(SV*, const char*); - void sv_setpvn(SV*, const char*, int) + void sv_setpvn(SV*, const char*, STRLEN) void sv_setpvf(SV*, const char*, ...); void sv_vsetpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool *); void sv_setsv(SV*, SV*); @@ -86,10 +91,6 @@ L). This pointer may be NULL if that information is not important. Note that this function requires you to specify the length of the format. -STRLEN is an integer type (Size_t, usually defined as size_t in -config.h) guaranteed to be large enough to represent the size of -any string that perl can handle. - The C functions are not generic enough to operate on values that have "magic". See L later in this document. @@ -199,12 +200,12 @@ you can call: SvOK(SV*) -The scalar C value is stored in an SV instance called C. Its -address can be used whenever an C is needed. +The scalar C value is stored in an SV instance called C. +Its address can be used whenever an C is needed. -There are also the two values C and C, which contain Boolean -TRUE and FALSE values, respectively. Like C, their addresses can -be used whenever an C is needed. +There are also the two values C and C, which contain +boolean TRUE and FALSE values, respectively. Like C, their +addresses can be used whenever an C is needed. Do not be fooled into thinking that C<(SV *) 0> is the same as C<&PL_sv_undef>. Take this code: @@ -218,8 +219,8 @@ Take this code: This code tries to return a new SV (which contains the value 42) if it should return a real value, or undef otherwise. Instead it has returned a NULL pointer which, somewhere down the line, will cause a segmentation violation, -bus error, or just weird results. Change the zero to C<&PL_sv_undef> in the first -line and all will be well. +bus error, or just weird results. Change the zero to C<&PL_sv_undef> in the +first line and all will be well. To free an SV that you've created, call C. Normally this call is not necessary (see L). @@ -536,7 +537,7 @@ The most useful types that will be returned are: =head2 Blessed References and Class Objects -References are also used to support object-oriented programming. In the +References are also used to support object-oriented programming. In perl's 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. @@ -545,8 +546,8 @@ A reference can be blessed into a package with the following function: SV* sv_bless(SV* sv, HV* stash); -The C argument must be a reference. The C argument specifies -which class the reference will belong to. See +The C argument must be a reference value. The C argument +specifies which class the reference will belong to. See L for information on converting class names into stashes. /* Still under construction */ @@ -685,9 +686,9 @@ later be decremented twice. "Mortal" SVs are mainly used for SVs that are placed on perl's stack. For example an SV which is created just to pass a number to a called sub -is made mortal to have it cleaned up automatically when stack is popped. -Similarly results returned by XSUBs (which go in the stack) are often -made mortal. +is made mortal to have it cleaned up automatically when it's popped off +the stack. Similarly, results returned by XSUBs (which are pushed on the +stack) are often made mortal. To create a mortal variable, use the functions: @@ -724,8 +725,8 @@ C or C routines. =head2 Stashes and Globs -A "stash" is a hash that contains all of the different objects that -are contained within a package. Each key of the stash is a symbol +A B is a hash that contains all variables that are defined +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, @@ -738,11 +739,11 @@ including (but not limited to) the following: Format Subroutine -There is a single stash called "PL_defstash" that holds the items that exist -in the "main" package. To get at the items in other packages, append the -string "::" to the package name. The items in the "Foo" package are in -the stash "Foo::" in PL_defstash. The items in the "Bar::Baz" package are -in the stash "Baz::" in "Bar::"'s stash. +There is a single stash called C that holds the items that exist +in the C
package. To get at the items in other packages, append the +string "::" to the package name. The items in the C package are in +the stash C in PL_defstash. The items in the C package are +in the stash C in C's stash. To get the stash pointer for a particular package, use the function: @@ -863,9 +864,9 @@ copy of the name is stored in C field. The sv_magic function uses C to determine which, if any, predefined "Magic Virtual Table" should be assigned to the C field. -See the "Magic Virtual Table" section below. The C argument is also +See the L section below. The C argument is also stored in the C field. The value of C should be chosen -from the set of macros C found perl.h. Note that before +from the set of macros C found in F. Note that before these macros were added, Perl internals used to directly use character literals, so you may occasionally come across old code or documentation referring to 'U' magic rather than C for example. @@ -904,7 +905,7 @@ The C has five pointers to the following routine types: int (*svt_clear)(SV* sv, MAGIC* mg); int (*svt_free)(SV* sv, MAGIC* mg); -This MGVTBL structure is set at compile-time in C and there are +This MGVTBL structure is set at compile-time in F 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. @@ -1324,7 +1325,8 @@ where C is the macro that represents the local copy of the stack pointer, and C is the number of elements the stack should be extended by. Now that there is room on the stack, values can be pushed on it using C -macro. The values pushed will often need to be "mortal" (See L). +macro. The pushed values will often need to be "mortal" (See +L). PUSHs(sv_2mortal(newSViv(an_integer))) PUSHs(sv_2mortal(newSVpv("Some String",0))) @@ -1394,6 +1396,8 @@ consult L. =head2 Memory Allocation +=head3 Allocation + All memory meant to be used with the Perl API functions should be manipulated using the macros described in this section. The macros provide the necessary transparency between differences in the actual malloc implementation that is @@ -1404,12 +1408,12 @@ 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. +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); -These three macros are used to initially allocate memory. - The first argument C was a "magic cookie" that was used to keep track of who called the macro, to help when debugging memory problems. However, the current code makes no use of this feature (most Perl developers now @@ -1427,6 +1431,8 @@ argument. Unlike the C and C macros, the C macro calls C to zero out all the newly allocated memory. +=head3 Reallocation + Renew(pointer, number, type); Renewc(pointer, number, type, cast); Safefree(pointer) @@ -1436,6 +1442,8 @@ piece of memory no longer needed. The arguments to C and C match those of C and C with the exception of not needing the "magic cookie" argument. +=head3 Moving + Move(source, dest, number, type); Copy(source, dest, number, type); Zero(dest, number, type); @@ -1564,8 +1572,8 @@ is the same as in our example. =head2 Examining the tree -If you have your perl compiled for debugging (usually done with C<-D -optimize=-g> on C command line), you may examine the +If you have your perl compiled for debugging (usually done with +C<-DDEBUGGING> on the C command line), you may examine the compiled tree by specifying C<-Dx> on the Perl command line. The output takes several lines per node, and for C<$b+$c> it looks like this: @@ -1634,6 +1642,9 @@ complicate matters, if a C is actually a C op after optimization (see L) it will still have children in accordance with its former type. +Another way to examine the tree is to use a compiler back-end module, such +as L. + =head2 Compile pass 1: check routines The tree is created by the compiler while I code feeds it @@ -2012,10 +2023,10 @@ more "hosts", with free association between them. =head1 Internal Functions All of Perl's internal functions which will be exposed to the outside -world are be prefixed by C so that they will not conflict with XS +world are prefixed by C so that they will not conflict with XS functions or functions used in a program in which Perl is embedded. Similarly, all global variables begin with C. (By convention, -static functions start with C) +static functions start with C.) Inside the Perl core, you can get at the functions either with or without the C prefix, thanks to a bunch of defines that live in