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-=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, const char *mode, PerlIO *old); /* deprecated */
- 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);
- int 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);
- int 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);
- int PerlIO_get_cnt(PerlIO *f);
- char *PerlIO_get_ptr(PerlIO *f);
- void PerlIO_set_ptrcnt(PerlIO *f, char *ptr, int 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);
- int 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_SFIO
-
-A "legacy" implementation in terms of the "sfio" library. Used for
-some specialist applications on Unix machines ("sfio" is not widely
-ported away from Unix). Most of above are #define'd to the sfio
-functions. PerlIO * is in this case Sfio_t *.
-
-=item 3. 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'} typical
-use might be
-
- Bourne shells (sh, ksh, bash, zsh, ash, ...):
- PERLIO_DEBUG=/dev/tty ./perl somescript some args
-
- Csh/Tcsh:
- setenv PERLIO_DEBUG /dev/tty
- ./perl somescript some args
-
- If you have the "env" utility:
- env PERLIO_DEBUG=/dev/tty ./perl somescript some args
-
- Win32:
- set PERLIO_DEBUG=CON
- perl somescript some args
-
-If $ENV{'PERLIO_DEBUG'} is not set PerlIO_debug() is a no-op.
-
-=back