FM / pod

/usr/share/perl5/pod

Name	Size	Mode	Actions
perl.pod	16270	0644	edit dl rm
perl56delta.pod	107201	0644	edit dl rm
perl58delta.pod	115165	0644	edit dl rm
perl561delta.pod	124713	0644	edit dl rm
perl581delta.pod	38061	0644	edit dl rm
perl582delta.pod	4470	0644	edit dl rm
perl583delta.pod	6335	0644	edit dl rm
perl584delta.pod	7363	0644	edit dl rm
perl585delta.pod	5889	0644	edit dl rm
perl586delta.pod	4651	0644	edit dl rm
perl587delta.pod	8357	0644	edit dl rm
perl588delta.pod	25272	0644	edit dl rm
perl589delta.pod	53900	0644	edit dl rm
perl5004delta.pod	56240	0644	edit dl rm
perl5005delta.pod	34283	0644	edit dl rm
perl5100delta.pod	55535	0644	edit dl rm
perl5101delta.pod	43888	0644	edit dl rm
perl5120delta.pod	89272	0644	edit dl rm
perl5121delta.pod	10141	0644	edit dl rm
perl5122delta.pod	9603	0644	edit dl rm
perl5123delta.pod	4100	0644	edit dl rm
perl5124delta.pod	3672	0644	edit dl rm
perl5125delta.pod	7683	0644	edit dl rm
perl5140delta.pod	144324	0644	edit dl rm
perl5141delta.pod	7966	0644	edit dl rm
perl5142delta.pod	6892	0644	edit dl rm
perl5143delta.pod	7760	0644	edit dl rm
perl5144delta.pod	6327	0644	edit dl rm
perl5160delta.pod	133651	0644	edit dl rm
perl5161delta.pod	6142	0644	edit dl rm
perl5162delta.pod	3594	0644	edit dl rm
perl5163delta.pod	4085	0644	edit dl rm
perl5180delta.pod	119431	0644	edit dl rm
perl5181delta.pod	6595	0644	edit dl rm
perl5182delta.pod	5335	0644	edit dl rm
perl5184delta.pod	4642	0644	edit dl rm
perl5200delta.pod	115699	0644	edit dl rm
perl5201delta.pod	10899	0644	edit dl rm
perl5202delta.pod	12509	0644	edit dl rm
perl5203delta.pod	9392	0644	edit dl rm
perl5220delta.pod	130963	0644	edit dl rm
perl5221delta.pod	10767	0644	edit dl rm
perl5222delta.pod	12629	0644	edit dl rm
perl5223delta.pod	8456	0644	edit dl rm
perl5224delta.pod	4460	0644	edit dl rm
perl5240delta.pod	64927	0644	edit dl rm
perl5241delta.pod	8215	0644	edit dl rm
perl5242delta.pod	4113	0644	edit dl rm
perl5243delta.pod	11428	0644	edit dl rm
perl5244delta.pod	4510	0644	edit dl rm
perl5260delta.pod	101836	0644	edit dl rm
perl5261delta.pod	7927	0644	edit dl rm
perl5262delta.pod	7880	0644	edit dl rm
perl5263delta.pod	7063	0644	edit dl rm
perl5280delta.pod	72113	0644	edit dl rm
perlaix.pod	20437	0644	edit dl rm
perlamiga.pod	5749	0644	edit dl rm
perlandroid.pod	7871	0644	edit dl rm
perlapi.pod	443535	0644	edit dl rm
perlapio.pod	19285	0644	edit dl rm
perlartistic.pod	7010	0644	edit dl rm
perlbook.pod	8338	0644	edit dl rm
perlboot.pod	294	0644	edit dl rm
perlbot.pod	304	0644	edit dl rm
perlbs2000.pod	8058	0644	edit dl rm
perlcall.pod	56706	0644	edit dl rm
perlce.pod	14602	0644	edit dl rm
perlcheat.pod	4481	0644	edit dl rm
perlclib.pod	9619	0644	edit dl rm
perlcn.pod	4691	0644	edit dl rm
perlcommunity.pod	7217	0644	edit dl rm
perlcygwin.pod	27199	0644	edit dl rm
perldata.pod	46743	0644	edit dl rm
perldbmfilter.pod	4981	0644	edit dl rm
perldebguts.pod	38535	0644	edit dl rm
perldebtut.pod	22152	0644	edit dl rm
perldebug.pod	39258	0644	edit dl rm
perldelta.pod	7063	0644	edit dl rm
perldeprecation.pod	18169	0644	edit dl rm
perldiag.pod	284572	0644	edit dl rm
perldos.pod	10522	0644	edit dl rm
perldsc.pod	25614	0644	edit dl rm
perldtrace.pod	7958	0644	edit dl rm
perlebcdic.pod	84233	0644	edit dl rm
perlembed.pod	37196	0644	edit dl rm
perlexperiment.pod	7195	0644	edit dl rm
perlfork.pod	13355	0644	edit dl rm
perlform.pod	16608	0644	edit dl rm
perlfreebsd.pod	1610	0644	edit dl rm
perlfunc.pod	392957	0644	edit dl rm
perlgit.pod	33509	0644	edit dl rm
perlgpl.pod	13815	0644	edit dl rm
perlguts.pod	139329	0644	edit dl rm
perlhack.pod	40445	0644	edit dl rm
perlhacktips.pod	55509	0644	edit dl rm
perlhacktut.pod	6153	0644	edit dl rm
perlhaiku.pod	1508	0644	edit dl rm
perlhist.pod	53546	0644	edit dl rm
perlhpux.pod	30509	0644	edit dl rm
perlhurd.pod	1993	0644	edit dl rm
perlintern.pod	54572	0644	edit dl rm
perlinterp.pod	33687	0644	edit dl rm
perlintro.pod	22119	0644	edit dl rm
perliol.pod	34185	0644	edit dl rm
perlipc.pod	70829	0644	edit dl rm
perlirix.pod	4395	0644	edit dl rm
perljp.pod	7521	0644	edit dl rm
perlko.pod	12259	0644	edit dl rm
perllexwarn.pod	355	0644	edit dl rm
perllinux.pod	1488	0644	edit dl rm
perllocale.pod	68678	0644	edit dl rm
perllol.pod	9580	0644	edit dl rm
perlmacos.pod	1001	0644	edit dl rm
perlmacosx.pod	12060	0644	edit dl rm
perlmod.pod	26250	0644	edit dl rm
perlmodinstall.pod	12792	0644	edit dl rm
perlmodlib.pod	76482	0644	edit dl rm
perlmodstyle.pod	22575	0644	edit dl rm
perlmroapi.pod	3212	0644	edit dl rm
perlnetware.pod	6648	0644	edit dl rm
perlnewmod.pod	11036	0644	edit dl rm
perlnumber.pod	8353	0644	edit dl rm
perlobj.pod	35537	0644	edit dl rm
perlootut.pod	26783	0644	edit dl rm
perlop.pod	136252	0644	edit dl rm
perlopenbsd.pod	1204	0644	edit dl rm
perlopentut.pod	9455	0644	edit dl rm
perlos2.pod	93351	0644	edit dl rm
perlos390.pod	15674	0644	edit dl rm
perlos400.pod	4768	0644	edit dl rm
perlpacktut.pod	51282	0644	edit dl rm
perlperf.pod	49881	0644	edit dl rm
perlplan9.pod	5125	0644	edit dl rm
perlpod.pod	22196	0644	edit dl rm
perlpodspec.pod	68476	0644	edit dl rm
perlpolicy.pod	25629	0644	edit dl rm
perlport.pod	87602	0644	edit dl rm
perlpragma.pod	5176	0644	edit dl rm
perlqnx.pod	6673	0644	edit dl rm
perlre.pod	120901	0644	edit dl rm
perlreapi.pod	30334	0644	edit dl rm
perlrebackslash.pod	31817	0644	edit dl rm
perlrecharclass.pod	49029	0644	edit dl rm
perlref.pod	35304	0644	edit dl rm
perlreftut.pod	18790	0644	edit dl rm
perlreguts.pod	38328	0644	edit dl rm
perlrepository.pod	509	0644	edit dl rm
perlrequick.pod	18497	0644	edit dl rm
perlreref.pod	14744	0644	edit dl rm
perlretut.pod	121257	0644	edit dl rm
perlriscos.pod	1529	0644	edit dl rm
perlrun.pod	53550	0644	edit dl rm
perlsec.pod	26184	0644	edit dl rm
perlsolaris.pod	29822	0644	edit dl rm
perlsource.pod	6876	0644	edit dl rm
perlstyle.pod	8630	0644	edit dl rm
perlsub.pod	72967	0644	edit dl rm
perlsymbian.pod	15359	0644	edit dl rm
perlsyn.pod	44512	0644	edit dl rm
perlsynology.pod	7778	0644	edit dl rm
perlthrtut.pod	46459	0644	edit dl rm
perltie.pod	38607	0644	edit dl rm
perltoc.pod	694171	0644	edit dl rm
perltodo.pod	376	0644	edit dl rm
perltooc.pod	294	0644	edit dl rm
perltoot.pod	294	0644	edit dl rm
perltrap.pod	10620	0644	edit dl rm
perltru64.pod	8492	0644	edit dl rm
perltw.pod	4477	0644	edit dl rm
perlunicode.pod	82491	0644	edit dl rm
perlunicook.pod	25488	0644	edit dl rm
perlunifaq.pod	13647	0644	edit dl rm
perluniintro.pod	38340	0644	edit dl rm
perluniprops.pod	285306	0644	edit dl rm
perlunitut.pod	7951	0644	edit dl rm
perlutil.pod	7640	0644	edit dl rm
perlvar.pod	78364	0644	edit dl rm
perlvms.pod	50823	0644	edit dl rm
perlvos.pod	3843	0644	edit dl rm
perlwin32.pod	39298	0644	edit dl rm
perlxs.pod	78920	0644	edit dl rm
perlxstut.pod	50095	0644	edit dl rm
perlxstypemap.pod	24001	0644	edit dl rm

Edit: /usr/share/perl5/pod/perlapio.pod (19285B)

=head1 NAME

perlapio - perl's IO abstraction interface.

=head1 SYNOPSIS

#define PERLIO_NOT_STDIO 0    /* For co-existence with stdio only */
  #include <perlio.h>           /* Usually via #include <perl.h> */

PerlIO *PerlIO_stdin(void);
  PerlIO *PerlIO_stdout(void);
  PerlIO *PerlIO_stderr(void);

PerlIO *PerlIO_open(const char *path,const char *mode);
  PerlIO *PerlIO_fdopen(int fd, const char *mode);
  PerlIO *PerlIO_reopen(const char *path, /* deprecated */
          const char *mode, PerlIO *old);
  int     PerlIO_close(PerlIO *f);

int     PerlIO_stdoutf(const char *fmt,...)
  int     PerlIO_puts(PerlIO *f,const char *string);
  int     PerlIO_putc(PerlIO *f,int ch);
  SSize_t PerlIO_write(PerlIO *f,const void *buf,size_t numbytes);
  int     PerlIO_printf(PerlIO *f, const char *fmt,...);
  int     PerlIO_vprintf(PerlIO *f, const char *fmt, va_list args);
  int     PerlIO_flush(PerlIO *f);

int     PerlIO_eof(PerlIO *f);
  int     PerlIO_error(PerlIO *f);
  void    PerlIO_clearerr(PerlIO *f);

int     PerlIO_getc(PerlIO *d);
  int     PerlIO_ungetc(PerlIO *f,int ch);
  SSize_t PerlIO_read(PerlIO *f, void *buf, size_t numbytes);

int     PerlIO_fileno(PerlIO *f);

void    PerlIO_setlinebuf(PerlIO *f);

Off_t   PerlIO_tell(PerlIO *f);
  int     PerlIO_seek(PerlIO *f, Off_t offset, int whence);
  void    PerlIO_rewind(PerlIO *f);

int     PerlIO_getpos(PerlIO *f, SV *save);    /* prototype changed */
  int     PerlIO_setpos(PerlIO *f, SV *saved);   /* prototype changed */

int     PerlIO_fast_gets(PerlIO *f);
  int     PerlIO_has_cntptr(PerlIO *f);
  SSize_t PerlIO_get_cnt(PerlIO *f);
  char   *PerlIO_get_ptr(PerlIO *f);
  void    PerlIO_set_ptrcnt(PerlIO *f, char *ptr, SSize_t count);

int     PerlIO_canset_cnt(PerlIO *f);              /* deprecated */
  void    PerlIO_set_cnt(PerlIO *f, int count);      /* deprecated */

int     PerlIO_has_base(PerlIO *f);
  char   *PerlIO_get_base(PerlIO *f);
  SSize_t PerlIO_get_bufsiz(PerlIO *f);

PerlIO *PerlIO_importFILE(FILE *stdio, const char *mode);
  FILE   *PerlIO_exportFILE(PerlIO *f, int flags);
  FILE   *PerlIO_findFILE(PerlIO *f);
  void    PerlIO_releaseFILE(PerlIO *f,FILE *stdio);

int     PerlIO_apply_layers(PerlIO *f, const char *mode,
                                                    const char *layers);
  int     PerlIO_binmode(PerlIO *f, int ptype, int imode,
                                                    const char *layers);
  void    PerlIO_debug(const char *fmt,...)

=head1 DESCRIPTION

Perl's source code, and extensions that want maximum portability,
should use the above functions instead of those defined in ANSI C's
I<stdio.h>.  The perl headers (in particular "perlio.h") will
C<#define> them to the I/O mechanism selected at Configure time.

The functions are modeled on those in I<stdio.h>, but parameter order
has been "tidied up a little".

C<PerlIO *> takes the place of FILE *. Like FILE * it should be
treated as opaque (it is probably safe to assume it is a pointer to
something).

There are currently three implementations:

=over 4

=item 1. USE_STDIO

All above are #define'd to stdio functions or are trivial wrapper
functions which call stdio. In this case I<only> PerlIO * is a FILE *.
This has been the default implementation since the abstraction was
introduced in perl5.003_02.

=item 2. USE_PERLIO

Introduced just after perl5.7.0, this is a re-implementation of the
above abstraction which allows perl more control over how IO is done
as it decouples IO from the way the operating system and C library
choose to do things. For USE_PERLIO PerlIO * has an extra layer of
indirection - it is a pointer-to-a-pointer.  This allows the PerlIO *
to remain with a known value while swapping the implementation around
underneath I<at run time>. In this case all the above are true (but
very simple) functions which call the underlying implementation.

This is the only implementation for which C<PerlIO_apply_layers()>
does anything "interesting".

The USE_PERLIO implementation is described in L<perliol>.

=back

Because "perlio.h" is a thin layer (for efficiency) the semantics of
these functions are somewhat dependent on the underlying implementation.
Where these variations are understood they are noted below.

Unless otherwise noted, functions return 0 on success, or a negative
value (usually C<EOF> which is usually -1) and set C<errno> on error.

=over 4

=item B<PerlIO_stdin()>, B<PerlIO_stdout()>, B<PerlIO_stderr()>

Use these rather than C<stdin>, C<stdout>, C<stderr>. They are written
to look like "function calls" rather than variables because this makes
it easier to I<make them> function calls if platform cannot export data
to loaded modules, or if (say) different "threads" might have different
values.

=item B<PerlIO_open(path, mode)>, B<PerlIO_fdopen(fd,mode)>

These correspond to fopen()/fdopen() and the arguments are the same.
Return C<NULL> and set C<errno> if there is an error.  There may be an
implementation limit on the number of open handles, which may be lower
than the limit on the number of open files - C<errno> may not be set
when C<NULL> is returned if this limit is exceeded.

=item B<PerlIO_reopen(path,mode,f)>

While this currently exists in all three implementations perl itself
does not use it. I<As perl does not use it, it is not well tested.>

Perl prefers to C<dup> the new low-level descriptor to the descriptor
used by the existing PerlIO. This may become the behaviour of this
function in the future.

=item B<PerlIO_printf(f,fmt,...)>, B<PerlIO_vprintf(f,fmt,a)>

These are fprintf()/vfprintf() equivalents.

=item B<PerlIO_stdoutf(fmt,...)>

This is printf() equivalent. printf is #defined to this function,
so it is (currently) legal to use C<printf(fmt,...)> in perl sources.

=item B<PerlIO_read(f,buf,count)>, B<PerlIO_write(f,buf,count)>

These correspond functionally to fread() and fwrite() but the
arguments and return values are different.  The PerlIO_read() and
PerlIO_write() signatures have been modeled on the more sane low level
read() and write() functions instead: The "file" argument is passed
first, there is only one "count", and the return value can distinguish
between error and C<EOF>.

Returns a byte count if successful (which may be zero or
positive), returns negative value and sets C<errno> on error.
Depending on implementation C<errno> may be C<EINTR> if operation was
interrupted by a signal.

=item B<PerlIO_close(f)>

Depending on implementation C<errno> may be C<EINTR> if operation was
interrupted by a signal.

=item B<PerlIO_puts(f,s)>, B<PerlIO_putc(f,c)>

These correspond to fputs() and fputc().
Note that arguments have been revised to have "file" first.

=item B<PerlIO_ungetc(f,c)>

This corresponds to ungetc().  Note that arguments have been revised
to have "file" first.  Arranges that next read operation will return
the byte B<c>.  Despite the implied "character" in the name only
values in the range 0..0xFF are defined. Returns the byte B<c> on
success or -1 (C<EOF>) on error.  The number of bytes that can be
"pushed back" may vary, only 1 character is certain, and then only if
it is the last character that was read from the handle.

=item B<PerlIO_getc(f)>

This corresponds to getc().
Despite the c in the name only byte range 0..0xFF is supported.
Returns the character read or -1 (C<EOF>) on error.

=item B<PerlIO_eof(f)>

This corresponds to feof().  Returns a true/false indication of
whether the handle is at end of file.  For terminal devices this may
or may not be "sticky" depending on the implementation.  The flag is
cleared by PerlIO_seek(), or PerlIO_rewind().

=item B<PerlIO_error(f)>

This corresponds to ferror().  Returns a true/false indication of
whether there has been an IO error on the handle.

=item B<PerlIO_fileno(f)>

This corresponds to fileno(), note that on some platforms, the meaning
of "fileno" may not match Unix. Returns -1 if the handle has no open
descriptor associated with it.

=item B<PerlIO_clearerr(f)>

This corresponds to clearerr(), i.e., clears 'error' and (usually)
'eof' flags for the "stream". Does not return a value.

=item B<PerlIO_flush(f)>

This corresponds to fflush().  Sends any buffered write data to the
underlying file.  If called with C<NULL> this may flush all open
streams (or core dump with some USE_STDIO implementations).  Calling
on a handle open for read only, or on which last operation was a read
of some kind may lead to undefined behaviour on some USE_STDIO
implementations.  The USE_PERLIO (layers) implementation tries to
behave better: it flushes all open streams when passed C<NULL>, and
attempts to retain data on read streams either in the buffer or by
seeking the handle to the current logical position.

=item B<PerlIO_seek(f,offset,whence)>

This corresponds to fseek().  Sends buffered write data to the
underlying file, or discards any buffered read data, then positions
the file descriptor as specified by B<offset> and B<whence> (sic).
This is the correct thing to do when switching between read and write
on the same handle (see issues with PerlIO_flush() above).  Offset is
of type C<Off_t> which is a perl Configure value which may not be same
as stdio's C<off_t>.

=item B<PerlIO_tell(f)>

This corresponds to ftell().  Returns the current file position, or
(Off_t) -1 on error.  May just return value system "knows" without
making a system call or checking the underlying file descriptor (so
use on shared file descriptors is not safe without a
PerlIO_seek()). Return value is of type C<Off_t> which is a perl
Configure value which may not be same as stdio's C<off_t>.

=item B<PerlIO_getpos(f,p)>, B<PerlIO_setpos(f,p)>

These correspond (loosely) to fgetpos() and fsetpos(). Rather than
stdio's Fpos_t they expect a "Perl Scalar Value" to be passed. What is
stored there should be considered opaque. The layout of the data may
vary from handle to handle.  When not using stdio or if platform does
not have the stdio calls then they are implemented in terms of
PerlIO_tell() and PerlIO_seek().

=item B<PerlIO_rewind(f)>

This corresponds to rewind(). It is usually defined as being

PerlIO_seek(f,(Off_t)0L, SEEK_SET);
    PerlIO_clearerr(f);

=item B<PerlIO_tmpfile()>

This corresponds to tmpfile(), i.e., returns an anonymous PerlIO or
NULL on error.  The system will attempt to automatically delete the
file when closed.  On Unix the file is usually C<unlink>-ed just after
it is created so it does not matter how it gets closed. On other
systems the file may only be deleted if closed via PerlIO_close()
and/or the program exits via C<exit>.  Depending on the implementation
there may be "race conditions" which allow other processes access to
the file, though in general it will be safer in this regard than
ad. hoc. schemes.

=item B<PerlIO_setlinebuf(f)>

This corresponds to setlinebuf().  Does not return a value. What
constitutes a "line" is implementation dependent but usually means
that writing "\n" flushes the buffer.  What happens with things like
"this\nthat" is uncertain.  (Perl core uses it I<only> when "dumping";
it has nothing to do with $| auto-flush.)

=back

=head2 Co-existence with stdio

There is outline support for co-existence of PerlIO with stdio.
Obviously if PerlIO is implemented in terms of stdio there is no
problem. However in other cases then mechanisms must exist to create a
FILE * which can be passed to library code which is going to use stdio
calls.

The first step is to add this line:

#define PERLIO_NOT_STDIO 0

I<before> including any perl header files. (This will probably become
the default at some point).  That prevents "perlio.h" from attempting
to #define stdio functions onto PerlIO functions.

XS code is probably better using "typemap" if it expects FILE *
arguments.  The standard typemap will be adjusted to comprehend any
changes in this area.

=over 4

=item B<PerlIO_importFILE(f,mode)>

Used to get a PerlIO * from a FILE *.

The mode argument should be a string as would be passed to
fopen/PerlIO_open.  If it is NULL then - for legacy support - the code
will (depending upon the platform and the implementation) either
attempt to empirically determine the mode in which I<f> is open, or
use "r+" to indicate a read/write stream.

Once called the FILE * should I<ONLY> be closed by calling
C<PerlIO_close()> on the returned PerlIO *.

The PerlIO is set to textmode. Use PerlIO_binmode if this is
not the desired mode.

This is B<not> the reverse of PerlIO_exportFILE().

=item B<PerlIO_exportFILE(f,mode)>

Given a PerlIO * create a 'native' FILE * suitable for passing to code
expecting to be compiled and linked with ANSI C I<stdio.h>.  The mode
argument should be a string as would be passed to fopen/PerlIO_open.
If it is NULL then - for legacy support - the FILE * is opened in same
mode as the PerlIO *.

The fact that such a FILE * has been 'exported' is recorded, (normally
by pushing a new :stdio "layer" onto the PerlIO *), which may affect
future PerlIO operations on the original PerlIO *.  You should not
call C<fclose()> on the file unless you call C<PerlIO_releaseFILE()>
to disassociate it from the PerlIO *.  (Do not use PerlIO_importFILE()
for doing the disassociation.)

Calling this function repeatedly will create a FILE * on each call
(and will push an :stdio layer each time as well).

=item B<PerlIO_releaseFILE(p,f)>

Calling PerlIO_releaseFILE informs PerlIO that all use of FILE * is
complete. It is removed from the list of 'exported' FILE *s, and the
associated PerlIO * should revert to its original behaviour.

Use this to disassociate a file from a PerlIO * that was associated
using PerlIO_exportFILE().

=item B<PerlIO_findFILE(f)>

Returns a native FILE * used by a stdio layer. If there is none, it
will create one with PerlIO_exportFILE. In either case the FILE *
should be considered as belonging to PerlIO subsystem and should
only be closed by calling C<PerlIO_close()>.

=back

=head2 "Fast gets" Functions

In addition to standard-like API defined so far above there is an
"implementation" interface which allows perl to get at internals of
PerlIO.  The following calls correspond to the various FILE_xxx macros
determined by Configure - or their equivalent in other
implementations. This section is really of interest to only those
concerned with detailed perl-core behaviour, implementing a PerlIO
mapping or writing code which can make use of the "read ahead" that
has been done by the IO system in the same way perl does. Note that
any code that uses these interfaces must be prepared to do things the
traditional way if a handle does not support them.

=over 4

=item B<PerlIO_fast_gets(f)>

Returns true if implementation has all the interfaces required to
allow perl's C<sv_gets> to "bypass" normal IO mechanism.  This can
vary from handle to handle.

PerlIO_fast_gets(f) = PerlIO_has_cntptr(f) && \
                        PerlIO_canset_cnt(f) && \
                        'Can set pointer into buffer'

=item B<PerlIO_has_cntptr(f)>

Implementation can return pointer to current position in the "buffer"
and a count of bytes available in the buffer.  Do not use this - use
PerlIO_fast_gets.

=item B<PerlIO_get_cnt(f)>

Return count of readable bytes in the buffer. Zero or negative return
means no more bytes available.

=item B<PerlIO_get_ptr(f)>

Return pointer to next readable byte in buffer, accessing via the
pointer (dereferencing) is only safe if PerlIO_get_cnt() has returned
a positive value.  Only positive offsets up to value returned by
PerlIO_get_cnt() are allowed.

=item B<PerlIO_set_ptrcnt(f,p,c)>

Set pointer into buffer, and a count of bytes still in the
buffer. Should be used only to set pointer to within range implied by
previous calls to C<PerlIO_get_ptr> and C<PerlIO_get_cnt>. The two
values I<must> be consistent with each other (implementation may only
use one or the other or may require both).

=item B<PerlIO_canset_cnt(f)>

Implementation can adjust its idea of number of bytes in the buffer.
Do not use this - use PerlIO_fast_gets.

=item B<PerlIO_set_cnt(f,c)>

Obscure - set count of bytes in the buffer. Deprecated.  Only usable
if PerlIO_canset_cnt() returns true.  Currently used in only doio.c to
force count less than -1 to -1.  Perhaps should be PerlIO_set_empty or
similar.  This call may actually do nothing if "count" is deduced from
pointer and a "limit".  Do not use this - use PerlIO_set_ptrcnt().

=item B<PerlIO_has_base(f)>

Returns true if implementation has a buffer, and can return pointer
to whole buffer and its size. Used by perl for B<-T> / B<-B> tests.
Other uses would be very obscure...

=item B<PerlIO_get_base(f)>

Return I<start> of buffer. Access only positive offsets in the buffer
up to the value returned by PerlIO_get_bufsiz().

=item B<PerlIO_get_bufsiz(f)>

Return the I<total number of bytes> in the buffer, this is neither the
number that can be read, nor the amount of memory allocated to the
buffer. Rather it is what the operating system and/or implementation
happened to C<read()> (or whatever) last time IO was requested.

=back

=head2 Other Functions

=over 4

=item PerlIO_apply_layers(f,mode,layers)

The new interface to the USE_PERLIO implementation. The layers ":crlf"
and ":raw" are only ones allowed for other implementations and those
are silently ignored. (As of perl5.8 ":raw" is deprecated.)  Use
PerlIO_binmode() below for the portable case.

=item PerlIO_binmode(f,ptype,imode,layers)

The hook used by perl's C<binmode> operator.
B<ptype> is perl's character for the kind of IO:

=over 8

=item 'E<lt>' read

=item 'E<gt>' write

=item '+' read/write

=back

B<imode> is C<O_BINARY> or C<O_TEXT>.

B<layers> is a string of layers to apply, only ":crlf" makes sense in
the non USE_PERLIO case. (As of perl5.8 ":raw" is deprecated in favour
of passing NULL.)

Portable cases are:

PerlIO_binmode(f,ptype,O_BINARY,NULL);
and
    PerlIO_binmode(f,ptype,O_TEXT,":crlf");

On Unix these calls probably have no effect whatsoever.  Elsewhere
they alter "\n" to CR,LF translation and possibly cause a special text
"end of file" indicator to be written or honoured on read. The effect
of making the call after doing any IO to the handle depends on the
implementation. (It may be ignored, affect any data which is already
buffered as well, or only apply to subsequent data.)

=item PerlIO_debug(fmt,...)

PerlIO_debug is a printf()-like function which can be used for
debugging.  No return value. Its main use is inside PerlIO where using
real printf, warn() etc. would recursively call PerlIO and be a
problem.

PerlIO_debug writes to the file named by $ENV{'PERLIO_DEBUG'} or defaults
to stderr if the environment variable is not defined. Typical
use might be

Bourne shells (sh, ksh, bash, zsh, ash, ...):
   PERLIO_DEBUG=/tmp/perliodebug.log ./perl -Di somescript some args

Csh/Tcsh:
   setenv PERLIO_DEBUG /tmp/perliodebug.log
   ./perl -Di somescript some args

If you have the "env" utility:
   env PERLIO_DEBUG=/tmp/perliodebug.log ./perl -Di somescript args

Win32:
   set PERLIO_DEBUG=perliodebug.log
   perl -Di somescript some args

On a Perl built without C<-DDEBUGGING>, or when the C<-Di> command-line switch
is not specified, or under taint, PerlIO_debug() is a no-op.

=back

cmd: