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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 implementattions). 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 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 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,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'} 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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