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man : B(3p)
ext::B::B(3p) Perl Programmers Reference Guide ext::B::B(3p)
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 knowledge of 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 back-
ends. This documentation assumes that the reader knows a
fair amount about perl's internals including such things
as SVs, OPs and the internal symbol table and syntax tree
of a program.
OVERVIEW
The "B" module contains a set of utility functions for
querying the current state of the Perl interpreter; typi-
cally these functions return objects 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.
Utility Functions
The "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.
Functions Returning "B::SV", "B::AV", "B::HV", and "B::CV"
objects
For descriptions of the class hierarchy of these objects
and the methods that can be called on them, see below,
"OVERVIEW OF CLASSES" and "SV-RELATED CLASSES".
sv_undef
Returns the SV object corresponding to the C variable
"sv_undef".
sv_yes
Returns the SV object corresponding to the C variable
"sv_yes".
sv_no
Returns the SV object corresponding to the C variable
"sv_no".
svref_2object(SVREF)
Takes a reference to any Perl value, and turns the
referred-to value into an object in the appropriate
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B::OP-derived or B::SV-derived class. Apart from func-
tions such as "main_root", 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 struc-
tures are freed.
amagic_generation
Returns the SV object corresponding to the C variable
"amagic_generation".
init_av
Returns the AV object (i.e. in class B::AV) represent-
ing INIT blocks.
check_av
Returns the AV object (i.e. in class B::AV) represent-
ing CHECK blocks.
begin_av
Returns the AV object (i.e. in class B::AV) represent-
ing BEGIN blocks.
end_av
Returns the AV object (i.e. in class B::AV) represent-
ing END blocks.
comppadlist
Returns the AV object (i.e. in class B::AV) of the
global comppadlist.
regex_padav
Only when perl was compiled with ithreads.
main_cv
Return the (faked) CV corresponding to the main part
of the Perl program.
Functions for Examining the Symbol Table
walksymtable(SYMREF, METHOD, RECURSE, PREFIX)
Walk the symbol table starting at SYMREF and call
METHOD on each symbol (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.
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For example:
# Walk CGI's symbol table calling print_subs on each symbol.
# Recurse only into CGI::Util::
walksymtable(\%CGI::, 'print_subs', sub { $_[0] eq 'CGI::Util::' },
'CGI::');
print_subs() is a B::GV method you have declared. Also
see "B::GV Methods", below.
Functions Returning "B::OP" objects or for walking op
trees
For descriptions of the class hierarchy of these objects
and the methods that can be called on them, see below,
"OVERVIEW OF CLASSES" and "OP-RELATED CLASSES".
main_root
Returns the root op (i.e. an object in the appropriate
B::OP-derived class) of the main part of the Perl pro-
gram.
main_start
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 vis-
ited before its children. If "walkoptree_debug" (see
below) has been called to turn debugging on then the
method "walkoptree_debug" is called on each op before
METHOD is called.
walkoptree_debug(DEBUG)
Returns the current debugging flag for "walkoptree".
If the optional DEBUG argument is non-zero, it sets
the debugging flag to that. See the description of
"walkoptree" above for what the debugging flag does.
Miscellaneous Utility Functions
ppname(OPNUM)
Return the PP function name (e.g. "pp_add") of op num-
ber OPNUM.
hash(STR)
Returns a string in the form "0x..." representing the
value of the internal hash function used by perl on
string STR.
cast_I32(I)
Casts I to the internal I32 type used by that perl.
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minus_c
Does 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
classname preceding the first "::". This is used to
turn "B::UNOP" into "UNOP" for example.
threadsv_names
In a perl compiled for threads, this returns a list of
the special per-thread threadsv variables.
OVERVIEW OF CLASSES
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 hierarchy and the "B" module gives
access to them via a true object hierarchy. Structure
fields which point to other objects (whether types of SV
or 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 cre-
ation doesn't increase the reference counts of the under-
lying objects. Trying to access the fields of a freed
object will give incomprehensible results, or worse.
SV-RELATED CLASSES
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 under-
lying C structures of similar names. The inheritance hier-
archy mimics the underlying C "inheritance". For 5.9.1 and
later this is:
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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 would cause 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
object_2svref
Returns a reference to the regular scalar correspond-
ing to this B::SV object. In other words, this method
is the inverse operation to the svref_2object() sub-
routine. This scalar and other data it points at
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should be considered read-only: modifying them is nei-
ther 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 & SVf_IVi-
sUV". Perhaps you want the "int_value" method instead?
IVX
UVX
int_value
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
packiv
B::NV Methods
NV
NVX
B::RV Methods
RV
B::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 reference.
PVX This method is less often useful. It assumes that the
string stored in the struct is null-terminated, and
disregards the length information.
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.
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B::PVMG Methods
MAGIC
SvSTASH
B::MAGIC Methods
MOREMAGIC
precomp
Only valid on r-magic, returns the string that gener-
ated the regexp.
PRIVATE
TYPE
FLAGS
OBJ Will die() if called on r-magic.
PTR
REGEX
Only valid on r-magic, returns the integer value of
the REGEX stored in the MAGIC.
B::PVLV Methods
TARGOFF
TARGLEN
TYPE
TARG
B::BM Methods
USEFUL
PREVIOUS
RARE
TABLE
B::GV Methods
is_empty
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 character of the name is a control character,
then it converts it to ^X first, so that *^G would
return "^G" rather than "\cG".
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It's useful if you want to print out the name of a
variable. If you restrict yourself to globs which
exist at compile-time then the result ought to be
unambiguous, because code like "${"^G"} = 1" is com-
piled 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
FLAGS
B::IO Methods
LINES
PAGE
PAGE_LEN
LINES_LEFT
TOP_NAME
TOP_GV
FMT_NAME
FMT_GV
BOTTOM_NAME
BOTTOM_GV
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 name was passed as argument ( i.e.
$io->IsSTD('stderr') is true if IoIFP($io) == Per-
lIO_stdin() ).
B::AV Methods
FILL
MAX
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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.
AvFLAGS
B::CV Methods
STASH
START
ROOT
GV
FILE
DEPTH
PADLIST
OUTSIDE
OUTSIDE_SEQ
XSUB
XSUBANY
For constant subroutines, returns the constant SV
returned by the subroutine.
CvFLAGS
const_sv
B::HV Methods
FILL
MAX
KEYS
RITER
NAME
PMROOT
ARRAY
OP-RELATED CLASSES
"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 under-
lying C structures of similar names. The inheritance hier-
archy mimics the underlying C "inheritance":
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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.
"PL_ppaddr[OP_ADD]", "PL_ppaddr[OP_RV2AV]").
desc
This returns the op description from the global C
PL_op_desc array (e.g. "addition" "array deref").
targ
type
opt
static
flags
private
spare
B::UNOP METHOD
first
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B::BINOP METHOD
last
B::LOGOP METHOD
other
B::LISTOP METHOD
children
B::PMOP Methods
pmreplroot
pmreplstart
pmnext
pmregexp
pmflags
pmdynflags
pmpermflags
precomp
pmoffset
Only when perl was compiled with ithreads.
B::SVOP METHOD
sv
gv
B::PADOP METHOD
padix
B::PVOP METHOD
pv
B::LOOP Methods
redoop
nextop
lastop
B::COP Methods
label
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stash
stashpv
file
cop_seq
arybase
line
warnings
io
AUTHOR
Malcolm Beattie, "mbeattieATsable.uk"
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