perlapio



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 imple-
           mentation 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 implementa-
       tion.  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.

       PPeerrllIIOO_ssttddiinn(()), PPeerrllIIOO_ssttddoouutt(()), PPeerrllIIOO_ssttddeerrrr(())
           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 descrip-
           tor 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 argu-
           ments and return values are different.  The PerlIO_read() and Per-
           lIO_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 distin-
           guish 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).  Call-
           ing 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 desciptor 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 Per-
           lIO_seek()). Return value is of type "Off_t" which is a perl Con-
           figure 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 plat-
           form 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);

       PPeerrllIIOO_ttmmppffiillee(())
           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 Per-
           lIO_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.  Obvi-
       ously 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 * argu-
       ments.  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 "Per-
           lIO_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/Per-
           lIO_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, (nor-
           mally 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 "Per-
           lIO_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 han-
       dle 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 pre-
           vious calls to "PerlIO_get_ptr" and "PerlIO_get_cnt". The two val-
           ues 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 Per-
           lIO_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 implementa-
           tion 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 depre-
           cated.)  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 char-
           acter 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,Nullch);
           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’} typi-
           cal 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 v5.8.6                       2004-11-05                       PERLAPIO(1)

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