NAME
B - The Perl Compiler
SYNOPSIS
use B;
DESCRIPTION
The "B" module supplies classes which allow a Perl program to delve
into its own innards. It is the module used to implement the "backends" of the Perl compiler. Usage of the compiler does not require knowledgeof this module: see the O module for the user-visible part. The "B"
module is of use to those who want to write new compiler backends. This documentation assumes that the reader knows a fair amount about perl'sinternals including such things as SVs, OPs and the internal symbol ta-
ble and syntax tree of a program. OOVVEERRVVIIEEWWThe "B" module contains a set of utility functions for querying the
current state of the Perl interpreter; typically these functions returnobjects from the B::SV and B::OP classes, or their derived classes.
These classes in turn define methods for querying the resulting objects about their own internal state. UUttiilliittyy FFuunnccttiioonnssThe "B" module exports a variety of functions: some are simple utility
functions, others provide a Perl program with a way to get an initial "handle" on an internal object.FFuunnccttiioonnss RReettuurrnniinngg ""BB::::SSVV"", "B::AV", "B::HV", and "B::CV" objects
For descriptions of the class hierarchy of these objects and the meth-
ods that can be called on them, see below, "OVERVIEW OF CLASSES" and"SV-RELATED CLASSES".
svundef Returns the SV object corresponding to the C variable "svundef". svyes Returns the SV object corresponding to the C variable "svyes". svno Returns the SV object corresponding to the C variable "svno". svref2object(SVREF)Takes a reference to any Perl value, and turns the referred-to
value into an object in the appropriate B::OP-derived or
B::SV-derived class. Apart from functions such as "mainroot", this
is the primary way to get an initial "handle" on an internal perl data structure which can then be followed with the other access methods. The returned object will only be valid as long as the underlying OPs and SVs continue to exist. Do not attempt to use the object after the underlying structures are freed. amagicgenerationReturns the SV object corresponding to the C variable "amagicgen-
eration". initavReturns the AV object (i.e. in class B::AV) representing INIT
blocks. checkavReturns the AV object (i.e. in class B::AV) representing CHECK
blocks. beginavReturns the AV object (i.e. in class B::AV) representing BEGIN
blocks. endavReturns the AV object (i.e. in class B::AV) representing END
blocks. comppadlistReturns the AV object (i.e. in class B::AV) of the global comp-
padlist. regexpadav Only when perl was compiled with ithreads. maincv Return the (faked) CV corresponding to the main part of the Perl program. FFuunnccttiioonnss ffoorr EExxaammiinniinngg tthhee SSyymmbbooll TTaabbllee walksymtable(SYMREF, METHOD, RECURSE, PREFIX) Walk the symbol table starting at SYMREF and call METHOD on eachsymbol (a B::GV object) visited. When the walk reaches package
symbols (such as "Foo::") it invokes RECURSE, passing in the symbol name, and only recurses into the package if that sub returns true. PREFIX is the name of the SYMREF you're walking. For example:# Walk CGI's symbol table calling printsubs on each symbol.
# Recurse only into CGI::Util::
walksymtable(\%CGI::, 'printsubs', sub { $[0] eq 'CGI::Util::' },
'CGI::');printsubs() is a B::GV method you have declared. Also see "B::GV
Methods", below.FFuunnccttiioonnss RReettuurrnniinngg ""BB::::OOPP"" oobbjjeeccttss oorr ffoorr wwaallkkiinngg oopp ttrreeeess
For descriptions of the class hierarchy of these objects and the meth-
ods that can be called on them, see below, "OVERVIEW OF CLASSES" and"OP-RELATED CLASSES".
mainroot Returns the root op (i.e. an object in the appropriateB::OP-derived class) of the main part of the Perl program.
mainstart Returns the starting op of the main part of the Perl program. walkoptree(OP, METHOD)Does a tree-walk of the syntax tree based at OP and calls METHOD on
each op it visits. Each node is visited before its children. If "walkoptreedebug" (see below) has been called to turn debugging on then the method "walkoptreedebug" is called on each op before METHOD is called.walkoptreedebug(DEBUG)
Returns the current debugging flag for "walkoptree". If theoptional DEBUG argument is non-zero, it sets the debugging flag to
that. See the description of "walkoptree" above for what the debug-
ging flag does. MMiisscceellllaanneeoouuss UUttiilliittyy FFuunnccttiioonnss ppname(OPNUM) Return the PP function name (e.g. "ppadd") of op number OPNUM. hash(STR) Returns a string in the form "0x..." representing the value of the internal hash function used by perl on string STR. castI32(I) Casts I to the internal I32 type used by that perl. minuscDoes the equivalent of the "-c" command-line option. Obviously,
this is only useful in a BEGIN block or else the flag is set too
late. cstring(STR)Returns a double-quote-surrounded escaped version of STR which can
be used as a string in C source code. perlstring(STR)Returns a double-quote-surrounded escaped version of STR which can
be used as a string in Perl source code.class(OBJ)
Returns the class of an object without the part of the classnamepreceding the first "::". This is used to turn "B::UNOP" into
"UNOP" for example. threadsvnames In a perl compiled for threads, this returns a list of the specialper-thread threadsv variables.
OOVVEERRVVIIEEWW OOFF CCLLAASSSSEESS The C structures used by Perl's internals to hold SV and OP information(PVIV, AV, HV, ..., OP, SVOP, UNOP, ...) are modelled on a class hier-
archy and the "B" module gives access to them via a true object hierar-
chy. Structure fields which point to other objects (whether types of SVor types of OP) are represented by the "B" module as Perl objects of
the appropriate class.The bulk of the "B" module is the methods for accessing fields of these
structures.Note that all access is read-only. You cannot modify the internals by
using this module. Also, note that the B::OP and B::SV objects created
by this module are only valid for as long as the underlying objects exist; their creation doesn't increase the reference counts of the underlying objects. Trying to access the fields of a freed object will give incomprehensible results, or worse.SSVV-RREELLAATTEEDD CCLLAASSSSEESS
B::IV, B::NV, B::RV, B::PV, B::PVIV, B::PVNV, B::PVMG, B::BM, B::PVLV,
B::AV, B::HV, B::CV, B::GV, B::FM, B::IO. These classes correspond in
the obvious way to the underlying C structures of similar names. The inheritance hierarchy mimics the underlying C "inheritance". For 5.9.1 and later this is:B::SV
|+-------+-----+------+
| | | |B::PV B::IV B::NV B::RV
\ / / \ / /B::PVIV /
\ / \ / \ /B::PVNV
| |B::PVMG
|+---+--+---+---+---+
| | | | | |B::BM B::AV B::GV B::HV B::CV B::IO
| |B::PVLV |
B::FM
For 5.9.0 and earlier, PVLV is a direct subclass of PVMG, so the base of this diagram is |B::PVMG
|+---+---+--+---+---+---+
| | | | | | |B::PVLV B::BM B::AV B::GV B::HV B::CV B::IO
| |B::FM
Access methods correspond to the underlying C macros for field access, usually with the leading "class indication" prefix removed (Sv, Av, Hv, ...). The leading prefix is only left in cases where its removal wouldcause a clash in method name. For example, "GvREFCNT" stays as-is since
its abbreviation would clash with the "superclass" method "REFCNT" (corresponding to the C function "SvREFCNT").B::SV Methods
REFCNT FLAGS object2svref Returns a reference to the regular scalar corresponding to thisB::SV object. In other words, this method is the inverse operation
to the svref2object() subroutine. This scalar and other data itpoints at should be considered read-only: modifying them is neither
safe nor guaranteed to have a sensible effect.B::IV Methods
IV Returns the value of the IV, interpreted as a signed integer. This will be misleading if "FLAGS & SVfIVisUV". Perhaps you want the "intvalue" method instead? IVX UVX intvalue This method returns the value of the IV as an integer. It differs from "IV" in that it returns the correct value regardless of whether it's stored signed or unsigned. needs64bits packivB::NV Methods
NV NVXB::RV Methods
RVB::PV Methods
PV This method is the one you usually want. It constructs a string using the length and offset information in the struct: for ordinary scalars it will return the string that you'd see from Perl, even if it contains null characters.RV Same as B::RV::RV, except that it will die() if the PV isn't a ref-
erence. PVX This method is less often useful. It assumes that the string storedin the struct is null-terminated, and disregards the length infor-
mation. It is the appropriate method to use if you need to get the name of a lexical variable from a padname array. Lexical variable names are always stored with a null terminator, and the length field (SvCUR) is overloaded for other purposes and can't be relied on here.B::PVMG Methods
MAGIC SvSTASHB::MAGIC Methods
MOREMAGIC precompOnly valid on r-magic, returns the string that generated the reg-
exp. PRIVATE TYPE FLAGSOBJ Will die() if called on r-magic.
PTR REGEXOnly valid on r-magic, returns the integer value of the REGEX
stored in the MAGIC.B::PVLV Methods
TARGOFF TARGLEN TYPE TARGB::BM Methods
USEFUL PREVIOUS RARETABLE
B::GV Methods
isempty This method returns TRUE if the GP field of the GV is NULL.NAME
SAFENAME
This method returns the name of the glob, but if the first charac-
ter of the name is a control character, then it converts it to ^X first, so that *^G would return "^G" rather than "\cG". It's useful if you want to print out the name of a variable. Ifyou restrict yourself to globs which exist at compile-time then the
result ought to be unambiguous, because code like "${"^G"} = 1" is
compiled as two ops - a constant string and a dereference (rv2gv) -
so that the glob is created at runtime. If you're working with globs at runtime, and need to disambiguate*^G from *{"^G"}, then you should use the raw NAME method.
STASH SV IO FORM AV HV EGV CV CVGEN LINE FILE FILEGV GvREFCNT FLAGSB::IO Methods
LINES PAGE PAGELEN LINESLEFTTOPNAME
TOPGVFMTNAME
FMTGVBOTTOMNAME
BOTTOMGV
SUBPROCESS
IoTYPE IoFLAGS IsSTD Takes one arguments ( 'stdin' | 'stdout' | 'stderr' ) and returns true if the IoIFP of the object is equal to the handle whose namewas passed as argument ( i.e. $io->IsSTD('stderr') is true if
IoIFP($io) == PerlIOstdin() ).
B::AV Methods
FILL MAX OFF ARRAY ARRAYelt Like "ARRAY", but takes an index as an argument to get only one element, rather than a list of all of them. AvFLAGSB::CV Methods
STASH START ROOT GV FILE DEPTH PADLIST OUTSIDE OUTSIDESEQXSUB
XSUBANY
For constant subroutines, returns the constant SV returned by the subroutine. CvFLAGS constsvB::HV Methods
FILL MAX KEYS RITERNAME
PMROOT ARRAYOOPP-RREELLAATTEEDD CCLLAASSSSEESS
"B::OP", "B::UNOP", "B::BINOP", "B::LOGOP", "B::LISTOP", "B::PMOP",
"B::SVOP", "B::PADOP", "B::PVOP", "B::LOOP", "B::COP".
These classes correspond in the obvious way to the underlying C struc-
tures of similar names. The inheritance hierarchy mimics the underlying C "inheritance":B::OP
|+--------+----+----+
| | | |B::UNOP B::SVOP B::PADOP B::COP
,' `-.
/ `-.
B::BINOP B::LOGOP
| |B::LISTOP
,' `. / \B::LOOP B::PMOP
Access methods correspond to the underlying C structre field names, with the leading "class indication" prefix ("op") removed.B::OP Methods
These methods get the values of similarly named fields within the OP data structure. See top of "op.h" for more info. next sibling name This returns the op name as a string (e.g. "add", "rv2av"). ppaddr This returns the function name as a string (e.g. "PLppaddr[OPADD]", "PLppaddr[OPRV2AV]"). desc This returns the op description from the global C PLopdesc array (e.g. "addition" "array deref"). targ type opt static flags private spareBB::::UUNNOOPP MMEETTHHOODD
firstBB::::BBIINNOOPP MMEETTHHOODD
lastBB::::LLOOGGOOPP MMEETTHHOODD
otherBB::::LLIISSTTOOPP MMEETTHHOODD
childrenB::PMOP Methods
pmreplroot pmreplstart pmnext pmregexp pmflags pmdynflags pmpermflags precomp pmoffset Only when perl was compiled with ithreads.BB::::SSVVOOPP MMEETTHHOODD
sv gvBB::::PPAADDOOPP MMEETTHHOODD
padixBB::::PPVVOOPP MMEETTHHOODD
pvB::LOOP Methods
redoop nextop lastopB::COP Methods
label stash stashpv file copseq arybase line warnings io AUTHORMalcolm Beattie, "mbeattie@sable.ox.ac.uk"
perl v5.8.8 2001-09-21 B(3pm)