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, /* deprecated */
const char *mode, PerlIO *old);
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);
SSize_t 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_fill(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);
SSize_t PerlIO_read(PerlIO *f, void *buf, size_t numbytes);
Size_t PerlIO_unread(PerlIO *f,const void *vbuf, size_t count
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);
SSize_t PerlIO_get_cnt(PerlIO *f);
char *PerlIO_get_ptr(PerlIO *f);
void PerlIO_set_ptrcnt(PerlIO *f, char *ptr, SSize_t 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);
SSize_t PerlIO_get_bufsiz(PerlIO *f);
PerlIO *PerlIO_importFILE(FILE *stdio, const char *mode);
FILE *PerlIO_exportFILE(PerlIO *f, const char *mode);
FILE *PerlIO_findFILE(PerlIO *f);
void PerlIO_releaseFILE(PerlIO *f,FILE *stdio);
int PerlIO_apply_layers(pTHX_ PerlIO *f, const char *mode,
const char *layers);
int PerlIO_binmode(pTHX_ 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 two 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_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 both 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_fill(f)
- Fills the buffer associated with "f"
with data from the layer below.
"PerlIO_read" calls this as part of its
normal operation. Returns 0 upon success; -1 on failure.
- 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_unread(f,buf,count)
- This allows one to unget more than a single byte. It effectively unshifts
"count" bytes onto the beginning of the
buffer "buf", so that the next read
operation(s) will return them before anything else that was in the buffer.
Returns the number of unread bytes.
- 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.)
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()".
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.
- PerlIO_apply_layers(aTHX_
f,mode,layers)
- The new interface to the USE_PERLIO implementation. The layers
":crlf" and ":raw" are the 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(aTHX_
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(aTHX_ f,ptype,O_BINARY,NULL);
and
PerlIO_binmode(aTHX_ 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'} or defaults to stderr if
the environment variable is not defined. Typical use might be
Bourne shells (sh, ksh, bash, zsh, ash, ...):
PERLIO_DEBUG=/tmp/perliodebug.log ./perl -Di somescript some args
Csh/Tcsh:
setenv PERLIO_DEBUG /tmp/perliodebug.log
./perl -Di somescript some args
If you have the "env" utility:
env PERLIO_DEBUG=/tmp/perliodebug.log ./perl -Di somescript args
Win32:
set PERLIO_DEBUG=perliodebug.log
perl -Di somescript some args
On a Perl built without
"-DDEBUGGING", or when the
"-Di" command-line switch is not
specified, or under taint, PerlIO_debug() is a no-op.