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.)

   #define PERLIO_NOT_STDIO 0

    PerlIO_binmode(f,ptype,O_BINARY,NULL);
and
    PerlIO_binmode(f,ptype,O_TEXT,":crlf");