perlapio.1

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.\" ========================================================================
.\"
.IX Title "PERLAPIO 1"
.TH PERLAPIO 1 "2007-12-18" "perl v5.10.0" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
perlapio \- perl's IO abstraction interface.
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\&    #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,...)
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
Perl's source code, and extensions that want maximum portability,
should use the above functions instead of those defined in \s-1ANSI\s0 C's
\&\fIstdio.h\fR.  The perl headers (in particular \*(L"perlio.h\*(R") will
\&\f(CW\*(C`#define\*(C'\fR them to the I/O mechanism selected at Configure time.
.PP
The functions are modeled on those in \fIstdio.h\fR, but parameter order
has been \*(L"tidied up a little\*(R".
.PP
\&\f(CW\*(C`PerlIO *\*(C'\fR takes the place of \s-1FILE\s0 *. Like \s-1FILE\s0 * it should be
treated as opaque (it is probably safe to assume it is a pointer to
something).
.PP
There are currently three implementations:
.IP "1. \s-1USE_STDIO\s0" 4
.IX Item "1. USE_STDIO"
All above are #define'd to stdio functions or are trivial wrapper
functions which call stdio. In this case \fIonly\fR PerlIO * is a \s-1FILE\s0 *.
This has been the default implementation since the abstraction was
introduced in perl5.003_02.
.IP "2. \s-1USE_SFIO\s0" 4
.IX Item "2. USE_SFIO"
A \*(L"legacy\*(R" implementation in terms of the \*(L"sfio\*(R" library. Used for
some specialist applications on Unix machines (\*(L"sfio\*(R" is not widely
ported away from Unix).  Most of above are #define'd to the sfio
functions. PerlIO * is in this case Sfio_t *.
.IP "3. \s-1USE_PERLIO\s0" 4
.IX 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 \s-1IO\s0 is done
as it decouples \s-1IO\s0 from the way the operating system and C library
choose to do things. For \s-1USE_PERLIO\s0 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 \fIat run time\fR. In this case all the above are true (but
very simple) functions which call the underlying implementation.
.Sp
This is the only implementation for which \f(CW\*(C`PerlIO_apply_layers()\*(C'\fR
does anything \*(L"interesting\*(R".
.Sp
The \s-1USE_PERLIO\s0 implementation is described in perliol.
.PP
Because \*(L"perlio.h\*(R" 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.
.PP
Unless otherwise noted, functions return 0 on success, or a negative
value (usually \f(CW\*(C`EOF\*(C'\fR which is usually \-1) and set \f(CW\*(C`errno\*(C'\fR on error.
.IP "\fB\f(BIPerlIO_stdin()\fB\fR, \fB\f(BIPerlIO_stdout()\fB\fR, \fB\f(BIPerlIO_stderr()\fB\fR" 4
.IX Item "PerlIO_stdin(), PerlIO_stdout(), PerlIO_stderr()"
Use these rather than \f(CW\*(C`stdin\*(C'\fR, \f(CW\*(C`stdout\*(C'\fR, \f(CW\*(C`stderr\*(C'\fR. They are written
to look like \*(L"function calls\*(R" rather than variables because this makes
it easier to \fImake them\fR function calls if platform cannot export data
to loaded modules, or if (say) different \*(L"threads\*(R" might have different
values.
.IP "\fBPerlIO_open(path, mode)\fR, \fBPerlIO_fdopen(fd,mode)\fR" 4
.IX Item "PerlIO_open(path, mode), PerlIO_fdopen(fd,mode)"
These correspond to \fIfopen()\fR/\fIfdopen()\fR and the arguments are the same.
Return \f(CW\*(C`NULL\*(C'\fR and set \f(CW\*(C`errno\*(C'\fR 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 \- \f(CW\*(C`errno\*(C'\fR may not be set
when \f(CW\*(C`NULL\*(C'\fR is returned if this limit is exceeded.
.IP "\fBPerlIO_reopen(path,mode,f)\fR" 4
.IX Item "PerlIO_reopen(path,mode,f)"
While this currently exists in all three implementations perl itself
does not use it. \fIAs perl does not use it, it is not well tested.\fR
.Sp
Perl prefers to \f(CW\*(C`dup\*(C'\fR the new low-level descriptor to the descriptor
used by the existing PerlIO. This may become the behaviour of this
function in the future.
.IP "\fBPerlIO_printf(f,fmt,...)\fR, \fBPerlIO_vprintf(f,fmt,a)\fR" 4
.IX Item "PerlIO_printf(f,fmt,...), PerlIO_vprintf(f,fmt,a)"
These are \fIfprintf()\fR/\fIvfprintf()\fR equivalents.
.IP "\fBPerlIO_stdoutf(fmt,...)\fR" 4
.IX Item "PerlIO_stdoutf(fmt,...)"
This is \fIprintf()\fR equivalent. printf is #defined to this function,
so it is (currently) legal to use \f(CW\*(C`printf(fmt,...)\*(C'\fR in perl sources.
.IP "\fBPerlIO_read(f,buf,count)\fR, \fBPerlIO_write(f,buf,count)\fR" 4
.IX Item "PerlIO_read(f,buf,count), PerlIO_write(f,buf,count)"
These correspond functionally to \fIfread()\fR and \fIfwrite()\fR but the
arguments and return values are different.  The \fIPerlIO_read()\fR and
\&\fIPerlIO_write()\fR signatures have been modeled on the more sane low level
\&\fIread()\fR and \fIwrite()\fR functions instead: The \*(L"file\*(R" argument is passed
first, there is only one \*(L"count\*(R", and the return value can distinguish
between error and \f(CW\*(C`EOF\*(C'\fR.
.Sp
Returns a byte count if successful (which may be zero or
positive), returns negative value and sets \f(CW\*(C`errno\*(C'\fR on error.
Depending on implementation \f(CW\*(C`errno\*(C'\fR may be \f(CW\*(C`EINTR\*(C'\fR if operation was
interrupted by a signal.
.IP "\fBPerlIO_close(f)\fR" 4
.IX Item "PerlIO_close(f)"
Depending on implementation \f(CW\*(C`errno\*(C'\fR may be \f(CW\*(C`EINTR\*(C'\fR if operation was
interrupted by a signal.
.IP "\fBPerlIO_puts(f,s)\fR, \fBPerlIO_putc(f,c)\fR" 4
.IX Item "PerlIO_puts(f,s), PerlIO_putc(f,c)"
These correspond to \fIfputs()\fR and \fIfputc()\fR.
Note that arguments have been revised to have \*(L"file\*(R" first.
.IP "\fBPerlIO_ungetc(f,c)\fR" 4
.IX Item "PerlIO_ungetc(f,c)"
This corresponds to \fIungetc()\fR.  Note that arguments have been revised