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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);



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           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.




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           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



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           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.



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       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



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           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



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           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.



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       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...





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       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.



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           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.






































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