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PERLAPIO(1)	       Perl Programmers Reference Guide		   PERLAPIO(1)

NAME
       perlapio - perl's IO abstraction interface.

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,...)

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

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

       "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:

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

       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 *.

       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 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 "PerlIO_apply_layers()"
	   does anything "interesting".

	   The USE_PERLIO implementation is described in perliol.

       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 "EOF" which is usually -1) and set "errno" on error.

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

       PerlIO_open(path, mode), PerlIO_fdopen(fd,mode)
	   These correspond to fopen()/fdopen() and the arguments are the
	   same.  Return "NULL" and set "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 - "errno"
	   may not be set when "NULL" is returned if this limit is exceeded.

       PerlIO_reopen(path,mode,f)
	   While this currently exists in all three implementations perl
	   itself does not use it. As perl does not use it, it is not well
	   tested.

	   Perl prefers to "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.

       PerlIO_printf(f,fmt,...), PerlIO_vprintf(f,fmt,a)
	   These are fprintf()/vfprintf() equivalents.

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

       PerlIO_read(f,buf,count), 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 "EOF".

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

       PerlIO_close(f)
	   Depending on implementation "errno" may be "EINTR" if operation was
	   interrupted by a signal.

       PerlIO_puts(f,s), PerlIO_putc(f,c)
	   These correspond to fputs() and fputc().  Note that arguments have
	   been revised to have "file" first.

       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 c.  Despite the implied "character" in the
	   name only values in the range 0..0xFF are defined. Returns the byte
	   c on success or -1 ("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.

       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
	   ("EOF") on error.

       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().

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

       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.

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

       PerlIO_flush(f)
	   This corresponds to fflush().  Sends any buffered write data to the
	   underlying file.  If called with "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
	   "NULL", and attempts to retain data on read streams either in the
	   buffer or by seeking the handle to the current logical position.

       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 offset and 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 "Off_t" which is a perl Configure value which may not be
	   same as stdio's "off_t".

       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 "Off_t" which is a perl
	   Configure value which may not be same as stdio's "off_t".

       PerlIO_getpos(f,p), 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().

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

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

       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 "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 "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.

       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 only when
	   "dumping"; it has nothing to do with $| auto-flush.)

   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

       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.

       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 f is
	   open, or use "r+" to indicate a read/write stream.

	   Once called the FILE * should ONLY be closed by calling
	   "PerlIO_close()" on the returned PerlIO *.

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

	   This is not the reverse of PerlIO_exportFILE().

       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 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 "fclose()" on the file unless you call
	   "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).

       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().

       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 "PerlIO_close()".

   "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.

       PerlIO_fast_gets(f)
	   Returns true if implementation has all the interfaces required to
	   allow perl's "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'

       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.

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

       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.

       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 "PerlIO_get_ptr" and "PerlIO_get_cnt". The two
	   values must be consistent with each other (implementation may only
	   use one or the other or may require both).

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

       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().

       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 -T / -B tests.
	   Other uses would be very obscure...

       PerlIO_get_base(f)
	   Return start of buffer. Access only positive offsets in the buffer
	   up to the value returned by PerlIO_get_bufsiz().

       PerlIO_get_bufsiz(f)
	   Return the 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 "read()" (or whatever) last time IO was
	   requested.

   Other Functions
       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.

       PerlIO_binmode(f,ptype,imode,layers)
	   The hook used by perl's "binmode" operator.	ptype is perl's
	   character for the kind of IO:

	   '<' read
	   '>' write
	   '+' read/write

	   imode is "O_BINARY" or "O_TEXT".

	   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.)

       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.

perl v5.10.1			  2009-02-12			   PERLAPIO(1)
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