perlintern - perldoc.perl.org

Perl Programming Documentation
Download Perl
Explore

Manual

- Overview
- Tutorials
- FAQs
- History / Changes
- License

Reference

- Language
- Functions
- Operators
- Special Variables
- Pragmas
- Utilities
- Internals
- Platform Specific

Modules

- A • B • C • D • E
- F • G • H • I • L
- M • N • O • P • S
- T • U • X

Tools

- Preferences

# perlintern

Perl 5 version 26.0 documentation
Go to top
Show page index • Show recent pages
Recently read

# perlintern

- NAME
- DESCRIPTION
- Compile-time scope hooks
- Custom Operators
- CV Manipulation Functions
- CV reference counts and CvOUTSIDE
- Embedding Functions
- GV Functions
- Hash Manipulation Functions
- IO Functions
- Lexer interface
- Magical Functions
- Miscellaneous Functions
- MRO Functions
- Optree Manipulation Functions
- Pad Data Structures
- Per-Interpreter Variables
- Stack Manipulation Macros
- SV-Body Allocation
- SV Manipulation Functions
- Unicode Support
- Undocumented functions
- AUTHORS
- SEE ALSO

# NAME

perlintern - autogenerated documentation of purely internal Perl functions

# DESCRIPTION

This file is the autogenerated documentation of functions in the Perl interpreter that are documented using Perl's internal documentation format but are not marked as part of the Perl API. In other words, they are not for use in extensions!

# Compile-time scope hooks

- BhkENTRY

  NOTE: this function is experimental and may change or be removed without notice.

  Return an entry from the BHK structure. `which` is a preprocessor token indicating which entry to return. If the appropriate flag is not set this will return `NULL` . The type of the return value depends on which entry you ask for.

      	void *	BhkENTRY(BHK *hk, which)

- BhkFLAGS

  NOTE: this function is experimental and may change or be removed without notice.

  Return the BHK's flags.

      	U32	BhkFLAGS(BHK *hk)

- CALL_BLOCK_HOOKS

  NOTE: this function is experimental and may change or be removed without notice.

  Call all the registered block hooks for type `which` . `which` is a preprocessing token; the type of `arg` depends on `which` .

      	void	CALL_BLOCK_HOOKS(which, arg)

# Custom Operators

- core_prototype

  This function assigns the prototype of the named core function to `sv` , or to a new mortal SV if `sv` is `NULL` . It returns the modified `sv` , or `NULL` if the core function has no prototype. `code` is a code as returned by `keyword()` . It must not be equal to 0.

      	SV *	core_prototype(SV *sv, const char *name,		               const int code,		               int * const opnum)

# CV Manipulation Functions

- docatch

  Check for the cases 0 or 3 of cur_env.je_ret, only used inside an eval context.

  0 is used as continue inside eval,

  3 is used for a die caught by an inner eval - continue inner loop

  See cop.h: je_mustcatch, when set at any runlevel to TRUE, means eval ops must establish a local jmpenv to handle exception traps.

      	OP*	docatch(OP *o)

# CV reference counts and CvOUTSIDE

- CvWEAKOUTSIDE

  Each CV has a pointer, `CvOUTSIDE()` , to its lexically enclosing CV (if any). Because pointers to anonymous sub prototypes are stored in `&` pad slots, it is a possible to get a circular reference, with the parent pointing to the child and vice-versa. To avoid the ensuing memory leak, we do not increment the reference count of the CV pointed to by `CvOUTSIDE` in the one specific instance that the parent has a `&` pad slot pointing back to us. In this case, we set the `CvWEAKOUTSIDE` flag in the child. This allows us to determine under what circumstances we should decrement the refcount of the parent when freeing the child.

  There is a further complication with non-closure anonymous subs (i.e. those that do not refer to any lexicals outside that sub). In this case, the anonymous prototype is shared rather than being cloned. This has the consequence that the parent may be freed while there are still active children, e.g.,

          BEGIN { $a = sub { eval '$x' } }

  In this case, the BEGIN is freed immediately after execution since there are no active references to it: the anon sub prototype has `CvWEAKOUTSIDE` set since it's not a closure, and $a points to the same CV, so it doesn't contribute to BEGIN's refcount either. When $a is executed, the `eval '$x'` causes the chain of `CvOUTSIDE` s to be followed, and the freed BEGIN is accessed.

  To avoid this, whenever a CV and its associated pad is freed, any `&` entries in the pad are explicitly removed from the pad, and if the refcount of the pointed-to anon sub is still positive, then that child's `CvOUTSIDE` is set to point to its grandparent. This will only occur in the single specific case of a non-closure anon prototype having one or more active references (such as `$a` above).

  One other thing to consider is that a CV may be merely undefined rather than freed, eg `undef &foo` . In this case, its refcount may not have reached zero, but we still delete its pad and its `CvROOT` etc. Since various children may still have their `CvOUTSIDE` pointing at this undefined CV, we keep its own `CvOUTSIDE` for the time being, so that the chain of lexical scopes is unbroken. For example, the following should print 123:

          my $x = 123;    sub tmp { sub { eval '$x' } }    my $a = tmp();    undef &tmp;    print  $a->();	bool	CvWEAKOUTSIDE(CV *cv)

# Embedding Functions

- cv_dump

  dump the contents of a CV

      	void	cv_dump(CV *cv, const char *title)

- cv_forget_slab

  When a CV has a reference count on its slab (`CvSLABBED` ), it is responsible for making sure it is freed. (Hence, no two CVs should ever have a reference count on the same slab.) The CV only needs to reference the slab during compilation. Once it is compiled and `CvROOT` attached, it has finished its job, so it can forget the slab.

      	void	cv_forget_slab(CV *cv)

- do_dump_pad

  Dump the contents of a padlist

      	void	do_dump_pad(I32 level, PerlIO *file,		            PADLIST *padlist, int full)

- pad_alloc_name

  Allocates a place in the currently-compiling pad (via pad_alloc in perlapi) and then stores a name for that entry. `name` is adopted and becomes the name entry; it must already contain the name string. `typestash` and `ourstash` and the `padadd_STATE` flag get added to `name` . None of the other processing of pad_add_name_pvn in perlapi is done. Returns the offset of the allocated pad slot.

      	PADOFFSET pad_alloc_name(PADNAME *name, U32 flags,	                         HV *typestash, HV *ourstash)

- pad_block_start

  Update the pad compilation state variables on entry to a new block.

      	void	pad_block_start(int full)

- pad_check_dup

  Check for duplicate declarations: report any of:

           * a 'my' in the current scope with the same name;     * an 'our' (anywhere in the pad) with the same name and the       same stash as 'ourstash'

  `is_our` indicates that the name to check is an `"our"` declaration.

      	void	pad_check_dup(PADNAME *name, U32 flags,		              const HV *ourstash)

- pad_findlex

  Find a named lexical anywhere in a chain of nested pads. Add fake entries in the inner pads if it's found in an outer one.

  Returns the offset in the bottom pad of the lex or the fake lex. `cv` is the CV in which to start the search, and seq is the current `cop_seq` to match against. If `warn` is true, print appropriate warnings. The `out_` * vars return values, and so are pointers to where the returned values should be stored. `out_capture` , if non-null, requests that the innermost instance of the lexical is captured; `out_name` is set to the innermost matched pad name or fake pad name; `out_flags` returns the flags normally associated with the `PARENT_FAKELEX_FLAGS` field of a fake pad name.

  Note that `pad_findlex()` is recursive; it recurses up the chain of CVs, then comes back down, adding fake entries as it goes. It has to be this way because fake names in anon protoypes have to store in `xpadn_low` the index into the parent pad.

      	PADOFFSET pad_findlex(const char *namepv,	                      STRLEN namelen, U32 flags,	                      const CV* cv, U32 seq, int warn,	                      SV** out_capture,	                      PADNAME** out_name,	                      int *out_flags)

- pad_fixup_inner_anons

  For any anon CVs in the pad, change `CvOUTSIDE` of that CV from `old_cv` to `new_cv` if necessary. Needed when a newly-compiled CV has to be moved to a pre-existing CV struct.

      	void	pad_fixup_inner_anons(PADLIST *padlist,		                      CV *old_cv, CV *new_cv)

- pad_free

  Free the SV at offset po in the current pad.

      	void	pad_free(PADOFFSET po)

- pad_leavemy

  Cleanup at end of scope during compilation: set the max seq number for lexicals in this scope and warn of any lexicals that never got introduced.

      	void	pad_leavemy()

- padlist_dup

  Duplicates a pad.

      	PADLIST * padlist_dup(PADLIST *srcpad,	                      CLONE_PARAMS *param)

- padname_dup

  Duplicates a pad name.

      	PADNAME * padname_dup(PADNAME *src, CLONE_PARAMS *param)

- padnamelist_dup

  Duplicates a pad name list.

      	PADNAMELIST * padnamelist_dup(PADNAMELIST *srcpad,	                              CLONE_PARAMS *param)

- pad_push

  Push a new pad frame onto the padlist, unless there's already a pad at this depth, in which case don't bother creating a new one. Then give the new pad an `@_` in slot zero.

      	void	pad_push(PADLIST *padlist, int depth)

- pad_reset

  Mark all the current temporaries for reuse

      	void	pad_reset()

- pad_swipe

  Abandon the tmp in the current pad at offset `po` and replace with a new one.

      	void	pad_swipe(PADOFFSET po, bool refadjust)

# GV Functions

- gv_try_downgrade

  NOTE: this function is experimental and may change or be removed without notice.

  If the typeglob `gv` can be expressed more succinctly, by having something other than a real GV in its place in the stash, replace it with the optimised form. Basic requirements for this are that `gv` is a real typeglob, is sufficiently ordinary, and is only referenced from its package. This function is meant to be used when a GV has been looked up in part to see what was there, causing upgrading, but based on what was found it turns out that the real GV isn't required after all.

  If `gv` is a completely empty typeglob, it is deleted from the stash.

  If `gv` is a typeglob containing only a sufficiently-ordinary constant sub, the typeglob is replaced with a scalar-reference placeholder that more compactly represents the same thing.

      	void	gv_try_downgrade(GV* gv)

# Hash Manipulation Functions

- hv_ename_add

  Adds a name to a stash's internal list of effective names. See `hv_ename_delete`.

  This is called when a stash is assigned to a new location in the symbol table.

      	void	hv_ename_add(HV *hv, const char *name, U32 len,		             U32 flags)

- hv_ename_delete

  Removes a name from a stash's internal list of effective names. If this is the name returned by `HvENAME` , then another name in the list will take its place (`HvENAME` will use it).

  This is called when a stash is deleted from the symbol table.

      	void	hv_ename_delete(HV *hv, const char *name,		                U32 len, U32 flags)

- refcounted_he_chain_2hv

  Generates and returns a `HV *` representing the content of a `refcounted_he` chain. `flags` is currently unused and must be zero.

      	HV *	refcounted_he_chain_2hv(		    const struct refcounted_he *c, U32 flags		)

- refcounted_he_fetch_pv

  Like refcounted_he_fetch_pvn, but takes a nul-terminated string instead of a string/length pair.

      	SV *	refcounted_he_fetch_pv(		    const struct refcounted_he *chain,		    const char *key, U32 hash, U32 flags		)

- refcounted_he_fetch_pvn

  Search along a `refcounted_he` chain for an entry with the key specified by `keypv` and `keylen` . If `flags` has the `REFCOUNTED_HE_KEY_UTF8` bit set, the key octets are interpreted as UTF-8, otherwise they are interpreted as Latin-1. `hash` is a precomputed hash of the key string, or zero if it has not been precomputed. Returns a mortal scalar representing the value associated with the key, or `&PL_sv_placeholder` if there is no value associated with the key.

      	SV *	refcounted_he_fetch_pvn(		    const struct refcounted_he *chain,		    const char *keypv, STRLEN keylen, U32 hash,		    U32 flags		)

- refcounted_he_fetch_pvs

  Like refcounted_he_fetch_pvn, but takes a `NUL` -terminated literal string instead of a string/length pair, and no precomputed hash.

      	SV *	refcounted_he_fetch_pvs(		    const struct refcounted_he *chain,		    const char *key, U32 flags		)

- refcounted_he_fetch_sv

  Like refcounted_he_fetch_pvn, but takes a Perl scalar instead of a string/length pair.

      	SV *	refcounted_he_fetch_sv(		    const struct refcounted_he *chain, SV *key,		    U32 hash, U32 flags		)

- refcounted_he_free

  Decrements the reference count of a `refcounted_he` by one. If the reference count reaches zero the structure's memory is freed, which (recursively) causes a reduction of its parent `refcounted_he` 's reference count. It is safe to pass a null pointer to this function: no action occurs in this case.

      	void	refcounted_he_free(struct refcounted_he *he)

- refcounted_he_inc

  Increment the reference count of a `refcounted_he` . The pointer to the `refcounted_he` is also returned. It is safe to pass a null pointer to this function: no action occurs and a null pointer is returned.

      	struct refcounted_he * refcounted_he_inc(	                           struct refcounted_he *he	                       )

- refcounted_he_new_pv

  Like refcounted_he_new_pvn, but takes a nul-terminated string instead of a string/length pair.

      	struct refcounted_he * refcounted_he_new_pv(	                           struct refcounted_he *parent,	                           const char *key, U32 hash,	                           SV *value, U32 flags	                       )

- refcounted_he_new_pvn

  Creates a new `refcounted_he` . This consists of a single key/value pair and a reference to an existing `refcounted_he` chain (which may be empty), and thus forms a longer chain. When using the longer chain, the new key/value pair takes precedence over any entry for the same key further along the chain.

  The new key is specified by `keypv` and `keylen` . If `flags` has the `REFCOUNTED_HE_KEY_UTF8` bit set, the key octets are interpreted as UTF-8, otherwise they are interpreted as Latin-1. `hash` is a precomputed hash of the key string, or zero if it has not been precomputed.

  `value` is the scalar value to store for this key. `value` is copied by this function, which thus does not take ownership of any reference to it, and later changes to the scalar will not be reflected in the value visible in the `refcounted_he` . Complex types of scalar will not be stored with referential integrity, but will be coerced to strings. `value` may be either null or `&PL_sv_placeholder` to indicate that no value is to be associated with the key; this, as with any non-null value, takes precedence over the existence of a value for the key further along the chain.

  `parent` points to the rest of the `refcounted_he` chain to be attached to the new `refcounted_he` . This function takes ownership of one reference to `parent` , and returns one reference to the new `refcounted_he` .

      	struct refcounted_he * refcounted_he_new_pvn(	                           struct refcounted_he *parent,	                           const char *keypv,	                           STRLEN keylen, U32 hash,	                           SV *value, U32 flags	                       )

- refcounted_he_new_pvs

  Like refcounted_he_new_pvn, but takes a `NUL` -terminated literal string instead of a string/length pair, and no precomputed hash.

      	struct refcounted_he * refcounted_he_new_pvs(	                           struct refcounted_he *parent,	                           const char *key, SV *value,	                           U32 flags	                       )

- refcounted_he_new_sv

  Like refcounted_he_new_pvn, but takes a Perl scalar instead of a string/length pair.

      	struct refcounted_he * refcounted_he_new_sv(	                           struct refcounted_he *parent,	                           SV *key, U32 hash, SV *value,	                           U32 flags	                       )

# IO Functions

- start_glob

  NOTE: this function is experimental and may change or be removed without notice.

  Function called by `do_readline` to spawn a glob (or do the glob inside perl on VMS). This code used to be inline, but now perl uses `File::Glob` this glob starter is only used by miniperl during the build process, or when PERL_EXTERNAL_GLOB is defined. Moving it away shrinks pp_hot.c; shrinking pp_hot.c helps speed perl up.

      	PerlIO*	start_glob(SV *tmpglob, IO *io)

# Lexer interface

- validate_proto

  NOTE: this function is experimental and may change or be removed without notice.

  This function performs syntax checking on a prototype, `proto` . If `warn` is true, any illegal characters or mismatched brackets will trigger illegalproto warnings, declaring that they were detected in the prototype for `name` .

  The return value is `true` if this is a valid prototype, and `false` if it is not, regardless of whether `warn` was `true` or `false` .

  Note that `NULL` is a valid `proto` and will always return `true` .

  NOTE: the perl_ form of this function is deprecated.

      	bool	validate_proto(SV *name, SV *proto, bool warn)

# Magical Functions

- magic_clearhint

  Triggered by a delete from `%^H` , records the key to `PL_compiling.cop_hints_hash` .

      	int	magic_clearhint(SV* sv, MAGIC* mg)

- magic_clearhints

  Triggered by clearing `%^H` , resets `PL_compiling.cop_hints_hash` .

      	int	magic_clearhints(SV* sv, MAGIC* mg)

- magic_methcall

  Invoke a magic method (like FETCH).

  `sv` and `mg` are the tied thingy and the tie magic.

  `meth` is the name of the method to call.

  `argc` is the number of args (in addition to $self) to pass to the method.

  The `flags` can be:

          G_DISCARD     invoke method with G_DISCARD flag and don't                  return a value    G_UNDEF_FILL  fill the stack with argc pointers to                  PL_sv_undef

  The arguments themselves are any values following the `flags` argument.

  Returns the SV (if any) returned by the method, or `NULL` on failure.

      	SV*	magic_methcall(SV *sv, const MAGIC *mg,		               SV *meth, U32 flags, U32 argc,		               ...)

- magic_sethint

  Triggered by a store to `%^H` , records the key/value pair to `PL_compiling.cop_hints_hash` . It is assumed that hints aren't storing anything that would need a deep copy. Maybe we should warn if we find a reference.

      	int	magic_sethint(SV* sv, MAGIC* mg)

- mg_localize

  Copy some of the magic from an existing SV to new localized version of that SV. Container magic (e.g., `%ENV` , `$1` , `tie`) gets copied, value magic doesn't (e.g., `taint` , `pos`).

  If `setmagic` is false then no set magic will be called on the new (empty) SV. This typically means that assignment will soon follow (e.g. `'local $x = $y'` ), and that will handle the magic.

      	void	mg_localize(SV* sv, SV* nsv, bool setmagic)

# Miscellaneous Functions

- free_c_backtrace

  Deallocates a backtrace received from get_c_bracktrace.

      	void	free_c_backtrace(Perl_c_backtrace* bt)

- get_c_backtrace

  Collects the backtrace (aka "stacktrace") into a single linear malloced buffer, which the caller must `Perl_free_c_backtrace()` .

  Scans the frames back by `depth + skip` , then drops the `skip` innermost, returning at most `depth` frames.

      	Perl_c_backtrace* get_c_backtrace(int max_depth,	                                  int skip)

# MRO Functions

- mro_get_linear_isa_dfs

  Returns the Depth-First Search linearization of `@ISA` the given stash. The return value is a read-only AV*. `level` should be 0 (it is used internally in this function's recursion).

  You are responsible for `SvREFCNT_inc()` on the return value if you plan to store it anywhere semi-permanently (otherwise it might be deleted out from under you the next time the cache is invalidated).

      	AV*	mro_get_linear_isa_dfs(HV* stash, U32 level)

- mro_isa_changed_in

  Takes the necessary steps (cache invalidations, mostly) when the `@ISA` of the given package has changed. Invoked by the `setisa` magic, should not need to invoke directly.

      	void	mro_isa_changed_in(HV* stash)

- mro_package_moved

  Call this function to signal to a stash that it has been assigned to another spot in the stash hierarchy. `stash` is the stash that has been assigned. `oldstash` is the stash it replaces, if any. `gv` is the glob that is actually being assigned to.

  This can also be called with a null first argument to indicate that `oldstash` has been deleted.

  This function invalidates isa caches on the old stash, on all subpackages nested inside it, and on the subclasses of all those, including non-existent packages that have corresponding entries in `stash` .

  It also sets the effective names (`HvENAME` ) on all the stashes as appropriate.

  If the `gv` is present and is not in the symbol table, then this function simply returns. This checked will be skipped if `flags & 1` .

      	void	mro_package_moved(HV * const stash,		                  HV * const oldstash,		                  const GV * const gv,		                  U32 flags)

# Optree Manipulation Functions

- finalize_optree

  This function finalizes the optree. Should be called directly after the complete optree is built. It does some additional checking which can't be done in the normal `ck_` xxx functions and makes the tree thread-safe.

      	void	finalize_optree(OP* o)

# Pad Data Structures

- CX_CURPAD_SAVE

  Save the current pad in the given context block structure.

      	void	CX_CURPAD_SAVE(struct context)

- CX_CURPAD_SV

  Access the SV at offset `po` in the saved current pad in the given context block structure (can be used as an lvalue).

      	SV *	CX_CURPAD_SV(struct context, PADOFFSET po)

- PAD_BASE_SV

  Get the value from slot `po` in the base (DEPTH=1) pad of a padlist

      	SV *	PAD_BASE_SV(PADLIST padlist, PADOFFSET po)

- PAD_CLONE_VARS

  Clone the state variables associated with running and compiling pads.

      	void	PAD_CLONE_VARS(PerlInterpreter *proto_perl,		               CLONE_PARAMS* param)

- PAD_COMPNAME_FLAGS

  Return the flags for the current compiling pad name at offset `po` . Assumes a valid slot entry.

      	U32	PAD_COMPNAME_FLAGS(PADOFFSET po)

- PAD_COMPNAME_GEN

  The generation number of the name at offset `po` in the current compiling pad (lvalue).

      	STRLEN	PAD_COMPNAME_GEN(PADOFFSET po)

- PAD_COMPNAME_GEN_set

  Sets the generation number of the name at offset `po` in the current ling pad (lvalue) to `gen` . STRLEN PAD_COMPNAME_GEN_set(PADOFFSET po, int gen)

- PAD_COMPNAME_OURSTASH

  Return the stash associated with an `our` variable. Assumes the slot entry is a valid `our` lexical.

      	HV *	PAD_COMPNAME_OURSTASH(PADOFFSET po)

- PAD_COMPNAME_PV

  Return the name of the current compiling pad name at offset `po` . Assumes a valid slot entry.

      	char *	PAD_COMPNAME_PV(PADOFFSET po)

- PAD_COMPNAME_TYPE

  Return the type (stash) of the current compiling pad name at offset `po` . Must be a valid name. Returns null if not typed.

      	HV *	PAD_COMPNAME_TYPE(PADOFFSET po)

- PadnameIsOUR

  Whether this is an "our" variable.

      	bool	PadnameIsOUR(PADNAME pn)

- PadnameIsSTATE

  Whether this is a "state" variable.

      	bool	PadnameIsSTATE(PADNAME pn)

- PadnameOURSTASH

  The stash in which this "our" variable was declared.

      	HV *	PadnameOURSTASH()

- PadnameOUTER

  Whether this entry belongs to an outer pad. Entries for which this is true are often referred to as 'fake'.

      	bool	PadnameOUTER(PADNAME pn)

- PadnameTYPE

  The stash associated with a typed lexical. This returns the `%Foo::` hash for `my Foo $bar` .

      	HV *	PadnameTYPE(PADNAME pn)

- PAD_RESTORE_LOCAL

  Restore the old pad saved into the local variable `opad` by `PAD_SAVE_LOCAL()`

      	void	PAD_RESTORE_LOCAL(PAD *opad)

- PAD_SAVE_LOCAL

  Save the current pad to the local variable `opad` , then make the current pad equal to `npad`

      	void	PAD_SAVE_LOCAL(PAD *opad, PAD *npad)

- PAD_SAVE_SETNULLPAD

  Save the current pad then set it to null.

      	void	PAD_SAVE_SETNULLPAD()

- PAD_SETSV

  Set the slot at offset `po` in the current pad to `sv`

      	SV *	PAD_SETSV(PADOFFSET po, SV* sv)

- PAD_SET_CUR

  Set the current pad to be pad `n` in the padlist, saving the previous current pad. NB currently this macro expands to a string too long for some compilers, so it's best to replace it with

          SAVECOMPPAD();    PAD_SET_CUR_NOSAVE(padlist,n);	void	PAD_SET_CUR(PADLIST padlist, I32 n)

- PAD_SET_CUR_NOSAVE

  like PAD_SET_CUR, but without the save

      	void	PAD_SET_CUR_NOSAVE(PADLIST padlist, I32 n)

- PAD_SV

  Get the value at offset `po` in the current pad

      	SV *	PAD_SV(PADOFFSET po)

- PAD_SVl

  Lightweight and lvalue version of `PAD_SV` . Get or set the value at offset `po` in the current pad. Unlike `PAD_SV` , does not print diagnostics with -DX. For internal use only.

      	SV *	PAD_SVl(PADOFFSET po)

- SAVECLEARSV

  Clear the pointed to pad value on scope exit. (i.e. the runtime action of `my`)

      	void	SAVECLEARSV(SV **svp)

- SAVECOMPPAD

  save `PL_comppad` and `PL_curpad`

      	void	SAVECOMPPAD()

- SAVEPADSV

  Save a pad slot (used to restore after an iteration)

  XXX DAPM it would make more sense to make the arg a PADOFFSET void SAVEPADSV(PADOFFSET po)

# Per-Interpreter Variables

- PL_DBsingle

  When Perl is run in debugging mode, with the -d switch, this SV is a boolean which indicates whether subs are being single-stepped. Single-stepping is automatically turned on after every step. This is the C variable which corresponds to Perl's $DB::single variable. See `PL_DBsub`.

      	SV *	PL_DBsingle

- PL_DBsub

  When Perl is run in debugging mode, with the -d switch, this GV contains the SV which holds the name of the sub being debugged. This is the C variable which corresponds to Perl's $DB::sub variable. See `PL_DBsingle`.

      	GV *	PL_DBsub

- PL_DBtrace

  Trace variable used when Perl is run in debugging mode, with the -d switch. This is the C variable which corresponds to Perl's $DB::trace variable. See `PL_DBsingle`.

      	SV *	PL_DBtrace

- PL_dowarn

  The C variable that roughly corresponds to Perl's `$^W` warning variable. However, `$^W` is treated as a boolean, whereas `PL_dowarn` is a collection of flag bits.

      	U8	PL_dowarn

- PL_last_in_gv

  The GV which was last used for a filehandle input operation. (`<FH>` )

      	GV*	PL_last_in_gv

- PL_ofsgv

  The glob containing the output field separator - `*,` in Perl space.

      	GV*	PL_ofsgv

- PL_rs

  The input record separator - `$/` in Perl space.

      	SV*	PL_rs

# Stack Manipulation Macros

- djSP

  Declare Just `SP` . This is actually identical to `dSP` , and declares a local copy of perl's stack pointer, available via the `SP` macro. See `SP in perlapi`. (Available for backward source code compatibility with the old (Perl 5.005) thread model.)

      		djSP;

- LVRET

  True if this op will be the return value of an lvalue subroutine

# SV-Body Allocation

- sv_2num

  NOTE: this function is experimental and may change or be removed without notice.

  Return an SV with the numeric value of the source SV, doing any necessary reference or overload conversion. The caller is expected to have handled get-magic already.

      	SV*	sv_2num(SV *const sv)

# SV Manipulation Functions

An SV (or AV, HV, etc.) is allocated in two parts: the head (struct sv, av, hv...) contains type and reference count information, and for many types, a pointer to the body (struct xrv, xpv, xpviv...), which contains fields specific to each type. Some types store all they need in the head, so don't have a body.

In all but the most memory-paranoid configurations (ex: PURIFY), heads and bodies are allocated out of arenas, which by default are approximately 4K chunks of memory parcelled up into N heads or bodies. Sv-bodies are allocated by their sv-type, guaranteeing size consistency needed to allocate safely from arrays.

For SV-heads, the first slot in each arena is reserved, and holds a link to the next arena, some flags, and a note of the number of slots. Snaked through each arena chain is a linked list of free items; when this becomes empty, an extra arena is allocated and divided up into N items which are threaded into the free list.

SV-bodies are similar, but they use arena-sets by default, which separate the link and info from the arena itself, and reclaim the 1st slot in the arena. SV-bodies are further described later.

The following global variables are associated with arenas:

     PL_sv_arenaroot     pointer to list of SV arenas PL_sv_root          pointer to list of free SV structures PL_body_arenas      head of linked-list of body arenas PL_body_roots[]     array of pointers to list of free bodies of svtype                     arrays are indexed by the svtype needed

A few special SV heads are not allocated from an arena, but are instead directly created in the interpreter structure, eg PL_sv_undef. The size of arenas can be changed from the default by setting PERL_ARENA_SIZE appropriately at compile time.

The SV arena serves the secondary purpose of allowing still-live SVs to be located and destroyed during final cleanup.

At the lowest level, the macros new_SV() and del_SV() grab and free an SV head. (If debugging with -DD, del_SV() calls the function S_del_sv() to return the SV to the free list with error checking.) new_SV() calls more_sv() / sv_add_arena() to add an extra arena if the free list is empty. SVs in the free list have their SvTYPE field set to all ones.

At the time of very final cleanup, sv_free_arenas() is called from perl_destruct() to physically free all the arenas allocated since the start of the interpreter.

The function visit() scans the SV arenas list, and calls a specified function for each SV it finds which is still live - ie which has an SvTYPE other than all 1's, and a non-zero SvREFCNT. visit() is used by the following functions (specified as [function that calls visit()] / [function called by visit() for each SV]):

        sv_report_used() / do_report_used()			dump all remaining SVs (debugging aid)    sv_clean_objs() / do_clean_objs(),do_clean_named_objs(),		      do_clean_named_io_objs(),do_curse()			Attempt to free all objects pointed to by RVs,			try to do the same for all objects indir-			ectly referenced by typeglobs too, and			then do a final sweep, cursing any			objects that remain.  Called once from			perl_destruct(), prior to calling sv_clean_all()			below.    sv_clean_all() / do_clean_all()			SvREFCNT_dec(sv) each remaining SV, possibly			triggering an sv_free(). It also sets the			SVf_BREAK flag on the SV to indicate that the			refcnt has been artificially lowered, and thus			stopping sv_free() from giving spurious warnings			about SVs which unexpectedly have a refcnt			of zero.  called repeatedly from perl_destruct()			until there are no SVs left.

- sv_add_arena

  Given a chunk of memory, link it to the head of the list of arenas, and split it into a list of free SVs.

      	void	sv_add_arena(char *const ptr, const U32 size,		             const U32 flags)

- sv_clean_all

  Decrement the refcnt of each remaining SV, possibly triggering a cleanup. This function may have to be called multiple times to free SVs which are in complex self-referential hierarchies.

      	I32	sv_clean_all()

- sv_clean_objs

  Attempt to destroy all objects not yet freed.

      	void	sv_clean_objs()

- sv_free_arenas

  Deallocate the memory used by all arenas. Note that all the individual SV heads and bodies within the arenas must already have been freed.

      	void	sv_free_arenas()

- SvTHINKFIRST

  A quick flag check to see whether an `sv` should be passed to `sv_force_normal` to be "downgraded" before `SvIVX` or `SvPVX` can be modified directly.

  For example, if your scalar is a reference and you want to modify the `SvIVX` slot, you can't just do `SvROK_off` , as that will leak the referent.

  This is used internally by various sv-modifying functions, such as `sv_setsv` , `sv_setiv` and `sv_pvn_force` .

  One case that this does not handle is a gv without SvFAKE set. After

          if (SvTHINKFIRST(gv)) sv_force_normal(gv);

  it will still be a gv.

  `SvTHINKFIRST` sometimes produces false positives. In those cases `sv_force_normal` does nothing.

      	U32	SvTHINKFIRST(SV *sv)

# Unicode Support

- find_uninit_var

  NOTE: this function is experimental and may change or be removed without notice.

  Find the name of the undefined variable (if any) that caused the operator to issue a "Use of uninitialized value" warning. If match is true, only return a name if its value matches `uninit_sv` . So roughly speaking, if a unary operator (such as `OP_COS` ) generates a warning, then following the direct child of the op may yield an `OP_PADSV` or `OP_GV` that gives the name of the undefined variable. On the other hand, with `OP_ADD` there are two branches to follow, so we only print the variable name if we get an exact match. `desc_p` points to a string pointer holding the description of the op. This may be updated if needed.

  The name is returned as a mortal SV.

  Assumes that `PL_op` is the OP that originally triggered the error, and that `PL_comppad` /`PL_curpad` points to the currently executing pad.

      	SV*	find_uninit_var(const OP *const obase,		                const SV *const uninit_sv,		                bool match, const char **desc_p)

- report_uninit

  Print appropriate "Use of uninitialized variable" warning.

      	void	report_uninit(const SV *uninit_sv)

# Undocumented functions

The following functions are currently undocumented. If you use one of them, you may wish to consider creating and submitting documentation for it.

- PerlIO_restore_errno
- PerlIO_save_errno
- Slab_Alloc
- Slab_Free
- Slab_to_ro
- Slab_to_rw
- _add_range_to_invlist
- _byte_dump_string
- _core_swash_init
- _get_regclass_nonbitmap_data
- _get_swash_invlist
- _invlistEQ
- _invlist_array_init
- _invlist_contains_cp
- _invlist_dump
- _invlist_intersection
- _invlist_intersection_maybe_complement_2nd
- _invlist_invert
- _invlist_len
- _invlist_populate_swatch
- _invlist_search
- _invlist_subtract
- _invlist_union
- _invlist_union_maybe_complement_2nd
- _is_grapheme
- _load_PL_utf8_foldclosures
- _mem_collxfrm
- _new_invlist
- _new_invlist_C_array
- _setup_canned_invlist
- _swash_inversion_hash
- _swash_to_invlist
- _to_fold_latin1
- _to_upper_title_latin1
- _warn_problematic_locale
- abort_execution
- add_cp_to_invlist
- alloc_LOGOP
- alloc_maybe_populate_EXACT
- allocmy
- amagic_is_enabled
- append_utf8_from_native_byte
- apply
- av_extend_guts
- av_reify
- bind_match
- boot_core_PerlIO
- boot_core_UNIVERSAL
- boot_core_mro
- cando
- check_utf8_print
- ck_anoncode
- ck_backtick
- ck_bitop
- ck_cmp
- ck_concat
- ck_defined
- ck_delete
- ck_each
- ck_entersub_args_core
- ck_eof
- ck_eval
- ck_exec
- ck_exists
- ck_ftst
- ck_fun
- ck_glob
- ck_grep
- ck_index
- ck_join
- ck_length
- ck_lfun
- ck_listiob
- ck_match
- ck_method
- ck_null
- ck_open
- ck_prototype
- ck_readline
- ck_refassign
- ck_repeat
- ck_require
- ck_return
- ck_rfun
- ck_rvconst
- ck_sassign
- ck_select
- ck_shift
- ck_smartmatch
- ck_sort
- ck_spair
- ck_split
- ck_stringify
- ck_subr
- ck_substr
- ck_svconst
- ck_tell
- ck_trunc
- closest_cop
- compute_EXACTish
- coresub_op
- create_eval_scope
- croak_caller
- croak_no_mem
- croak_popstack
- current_re_engine
- custom_op_get_field
- cv_ckproto_len_flags
- cv_clone_into
- cv_const_sv_or_av
- cv_undef_flags
- cvgv_from_hek
- cvgv_set
- cvstash_set
- deb_stack_all
- defelem_target
- delete_eval_scope
- delimcpy_no_escape
- die_unwind
- do_aexec
- do_aexec5
- do_eof
- do_exec
- do_exec3
- do_execfree
- do_ipcctl
- do_ipcget
- do_msgrcv
- do_msgsnd
- do_ncmp
- do_open6
- do_open_raw
- do_print
- do_readline
- do_seek
- do_semop
- do_shmio
- do_sysseek
- do_tell
- do_trans
- do_vecget
- do_vecset
- do_vop
- does_utf8_overflow
- dofile
- drand48_init_r
- drand48_r
- dtrace_probe_call
- dtrace_probe_load
- dtrace_probe_op
- dtrace_probe_phase
- dump_all_perl
- dump_packsubs_perl
- dump_sub_perl
- dump_sv_child
- emulate_cop_io
- feature_is_enabled
- find_lexical_cv
- find_runcv_where
- find_script
- form_short_octal_warning
- free_tied_hv_pool
- get_db_sub
- get_debug_opts
- get_hash_seed
- get_invlist_iter_addr
- get_invlist_offset_addr
- get_invlist_previous_index_addr
- get_no_modify
- get_opargs
- get_re_arg
- getenv_len
- grok_atoUV
- grok_bslash_c
- grok_bslash_o
- grok_bslash_x
- gv_fetchmeth_internal
- gv_override
- gv_setref
- gv_stashpvn_internal
- gv_stashsvpvn_cached
- handle_named_backref
- hfree_next_entry
- hv_backreferences_p
- hv_kill_backrefs
- hv_placeholders_p
- hv_undef_flags
- init_argv_symbols
- init_constants
- init_dbargs
- init_debugger
- invert
- invlist_array
- invlist_clear
- invlist_clone
- invlist_highest
- invlist_is_iterating
- invlist_iterfinish
- invlist_iterinit
- invlist_max
- invlist_previous_index
- invlist_set_len
- invlist_set_previous_index
- invlist_trim
- io_close
- isFF_OVERLONG
- isFOO_lc
- is_utf8_common
- is_utf8_common_with_len
- is_utf8_cp_above_31_bits
- is_utf8_overlong_given_start_byte_ok
- isinfnansv
- jmaybe
- keyword
- keyword_plugin_standard
- list
- localize
- magic_clear_all_env
- magic_cleararylen_p
- magic_clearenv
- magic_clearisa
- magic_clearpack
- magic_clearsig
- magic_copycallchecker
- magic_existspack
- magic_freearylen_p
- magic_freeovrld
- magic_get
- magic_getarylen
- magic_getdebugvar
- magic_getdefelem
- magic_getnkeys
- magic_getpack
- magic_getpos
- magic_getsig
- magic_getsubstr
- magic_gettaint
- magic_getuvar
- magic_getvec
- magic_killbackrefs
- magic_nextpack
- magic_regdata_cnt
- magic_regdatum_get
- magic_regdatum_set
- magic_scalarpack
- magic_set
- magic_set_all_env
- magic_setarylen
- magic_setcollxfrm
- magic_setdbline
- magic_setdebugvar
- magic_setdefelem
- magic_setenv
- magic_setisa
- magic_setlvref
- magic_setmglob
- magic_setnkeys
- magic_setpack
- magic_setpos
- magic_setregexp
- magic_setsig
- magic_setsubstr
- magic_settaint
- magic_setutf8
- magic_setuvar
- magic_setvec
- magic_sizepack
- magic_wipepack
- malloc_good_size
- malloced_size
- mem_collxfrm
- mem_log_alloc
- mem_log_free
- mem_log_realloc
- mg_find_mglob
- mode_from_discipline
- more_bodies
- mro_meta_dup
- mro_meta_init
- multideref_stringify
- my_attrs
- my_clearenv
- my_lstat_flags
- my_stat_flags
- my_unexec
- newATTRSUB_x
- newGP
- newMETHOP_internal
- newSTUB
- newSVavdefelem
- newXS_deffile
- newXS_len_flags
- new_warnings_bitfield
- nextargv
- noperl_die
- notify_parser_that_changed_to_utf8
- oopsAV
- oopsHV
- op_clear
- op_integerize
- op_lvalue_flags
- op_refcnt_dec
- op_refcnt_inc
- op_relocate_sv
- op_std_init
- op_unscope
- opmethod_stash
- opslab_force_free
- opslab_free
- opslab_free_nopad
- package
- package_version
- pad_add_weakref
- padlist_store
- padname_free
- padnamelist_free
- parse_unicode_opts
- parser_free
- parser_free_nexttoke_ops
- path_is_searchable
- peep
- pmruntime
- populate_isa
- ptr_hash
- qerror
- re_exec_indentf
- re_indentf
- re_op_compile
- re_printf
- reg_named_buff
- reg_named_buff_iter
- reg_numbered_buff_fetch
- reg_numbered_buff_length
- reg_numbered_buff_store
- reg_qr_package
- reg_skipcomment
- reg_temp_copy
- regcurly
- regprop
- report_evil_fh
- report_redefined_cv
- report_wrongway_fh
- rpeep
- rsignal_restore
- rsignal_save
- rxres_save
- same_dirent
- save_strlen
- sawparens
- scalar
- scalarvoid
- set_caret_X
- set_padlist
- should_warn_nl
- sighandler
- softref2xv
- ssc_add_range
- ssc_clear_locale
- ssc_cp_and
- ssc_intersection
- ssc_union
- sub_crush_depth
- sv_add_backref
- sv_buf_to_ro
- sv_del_backref
- sv_free2
- sv_kill_backrefs
- sv_len_utf8_nomg
- sv_magicext_mglob
- sv_mortalcopy_flags
- sv_only_taint_gmagic
- sv_or_pv_pos_u2b
- sv_resetpvn
- sv_sethek
- sv_setsv_cow
- sv_unglob
- swash_fetch
- swash_init
- tied_method
- tmps_grow_p
- translate_substr_offsets
- try_amagic_bin
- try_amagic_un
- unshare_hek
- utilize
- varname
- vivify_defelem
- vivify_ref
- wait4pid
- was_lvalue_sub
- watch
- win32_croak_not_implemented
- write_to_stderr
- xs_boot_epilog
- xs_handshake
- yyerror
- yyerror_pv
- yyerror_pvn
- yylex
- yyparse
- yyquit
- yyunlex

# AUTHORS

The autodocumentation system was originally added to the Perl core by Benjamin Stuhl. Documentation is by whoever was kind enough to document their functions.

# SEE ALSO

perlguts, perlapi

Page index

- NAME
- DESCRIPTION
- Compile-time scope hooks
- Custom Operators
- CV Manipulation Functions
- CV reference counts and CvOUTSIDE
- Embedding Functions
- GV Functions
- Hash Manipulation Functions
- IO Functions
- Lexer interface
- Magical Functions
- Miscellaneous Functions
- MRO Functions
- Optree Manipulation Functions
- Pad Data Structures
- Per-Interpreter Variables
- Stack Manipulation Macros
- SV-Body Allocation
- SV Manipulation Functions
- Unicode Support
- Undocumented functions
- AUTHORS
- SEE ALSO