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.)
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,NULL);
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.