perlapio - perl's IO abstraction interface.
#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,...)
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) [Toc] [Back]
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) [Toc] [Back]
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) [Toc] [Back]
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) [Toc] [Back]
This corresponds to ferror(). Returns a true/false
indication of whether there has been an IO error on
the handle.
PerlIO_fileno(f) [Toc] [Back]
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) [Toc] [Back]
This corresponds to clearerr(), i.e., clears 'error'
and (usually) 'eof' flags for the "stream". Does not
return a value.
PerlIO_flush(f) [Toc] [Back]
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) [Toc] [Back]
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 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 Per-
lIO_seek().
PerlIO_rewind(f) [Toc] [Back]
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) [Toc] [Back]
This corresponds to setlinebuf(). Does not return a
value. What constitutes a "line" is implementation
dependent but usually means that writing "0 flushes
the buffer. What happens with things like
"this0hat" is uncertain. (Perl core uses it only
when "dumping"; it has nothing to do with $|
auto-flush.)
Co-existence with stdio [Toc] [Back]
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) [Toc] [Back]
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) [Toc] [Back]
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) [Toc] [Back]
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) [Toc] [Back]
Return count of readable bytes in the buffer. Zero or
negative return means no more bytes available.
PerlIO_get_ptr(f) [Toc] [Back]
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 Per-
lIO_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) [Toc] [Back]
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) [Toc] [Back]
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) [Toc] [Back]
Return start of buffer. Access only positive offsets
in the buffer up to the value returned by Per-
lIO_get_bufsiz().
PerlIO_get_bufsiz(f) [Toc] [Back]
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 [Toc] [Back]
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 "0 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.
perl v5.8.5 2002-11-06 10 [ Back ] |
