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760ac839 1=head1 NAME
2
28757baa 3perlapio - perl's IO abstraction interface.
760ac839 4
5=head1 SYNOPSIS
6
3039a93d 7 #define PERLIO_NOT_STDIO 0 /* For co-existence with stdio only */
50b80e25 8 #include <perlio.h> /* Usually via #include <perl.h> */
9
760ac839 10 PerlIO *PerlIO_stdin(void);
11 PerlIO *PerlIO_stdout(void);
12 PerlIO *PerlIO_stderr(void);
54310121 13
50b80e25 14 PerlIO *PerlIO_open(const char *path,const char *mode);
15 PerlIO *PerlIO_fdopen(int fd, const char *mode);
16 PerlIO *PerlIO_reopen(const char *path, const char *mode, PerlIO *old); /* deprecated */
17 int PerlIO_close(PerlIO *f);
18
19 int PerlIO_stdoutf(const char *fmt,...)
20 int PerlIO_puts(PerlIO *f,const char *string);
21 int PerlIO_putc(PerlIO *f,int ch);
22 int PerlIO_write(PerlIO *f,const void *buf,size_t numbytes);
23 int PerlIO_printf(PerlIO *f, const char *fmt,...);
24 int PerlIO_vprintf(PerlIO *f, const char *fmt, va_list args);
25 int PerlIO_flush(PerlIO *f);
26
27 int PerlIO_eof(PerlIO *f);
28 int PerlIO_error(PerlIO *f);
29 void PerlIO_clearerr(PerlIO *f);
30
31 int PerlIO_getc(PerlIO *d);
32 int PerlIO_ungetc(PerlIO *f,int ch);
33 int PerlIO_read(PerlIO *f, void *buf, size_t numbytes);
34
35 int PerlIO_fileno(PerlIO *f);
36
37 void PerlIO_setlinebuf(PerlIO *f);
38
39 Off_t PerlIO_tell(PerlIO *f);
40 int PerlIO_seek(PerlIO *f, Off_t offset, int whence);
41 void PerlIO_rewind(PerlIO *f);
42
43 int PerlIO_getpos(PerlIO *f, SV *save); /* prototype changed */
44 int PerlIO_setpos(PerlIO *f, SV *saved); /* prototype changed */
45
46 int PerlIO_fast_gets(PerlIO *f);
47 int PerlIO_has_cntptr(PerlIO *f);
48 int PerlIO_get_cnt(PerlIO *f);
49 char *PerlIO_get_ptr(PerlIO *f);
50 void PerlIO_set_ptrcnt(PerlIO *f, char *ptr, int count);
51
52 int PerlIO_canset_cnt(PerlIO *f); /* deprecated */
53 void PerlIO_set_cnt(PerlIO *f, int count); /* deprecated */
54
55 int PerlIO_has_base(PerlIO *f);
56 char *PerlIO_get_base(PerlIO *f);
57 int PerlIO_get_bufsiz(PerlIO *f);
58
59 PerlIO *PerlIO_importFILE(FILE *stdio, int flags);
60 FILE *PerlIO_exportFILE(PerlIO *f, int flags);
61 FILE *PerlIO_findFILE(PerlIO *f);
62 void PerlIO_releaseFILE(PerlIO *f,FILE *stdio);
63
64 int PerlIO_apply_layers(PerlIO *f, const char *mode, const char *layers);
65 int PerlIO_binmode(PerlIO *f, int ptype, int imode, const char *layers);
66 void PerlIO_debug(const char *fmt,...)
760ac839 67
68=head1 DESCRIPTION
69
06936a3c 70Perl's source code, and extensions that want maximum portability,
71should use the above functions instead of those defined in ANSI C's
72I<stdio.h>. The perl headers (in particular "perlio.h") will
73C<#define> them to the I/O mechanism selected at Configure time.
760ac839 74
75The functions are modeled on those in I<stdio.h>, but parameter order
76has been "tidied up a little".
77
06936a3c 78C<PerlIO *> takes the place of FILE *. Like FILE * it should be
79treated as opaque (it is probably safe to assume it is a pointer to
80something).
50b80e25 81
82There are currently three implementations:
83
760ac839 84=over 4
85
50b80e25 86=item 1. USE_STDIO
760ac839 87
06936a3c 88All above are #define'd to stdio functions or are trivial wrapper
89functions which call stdio. In this case I<only> PerlIO * is a FILE *.
90This has been the default implementation since the abstraction was
91introduced in perl5.003_02.
50b80e25 92
93=item 2. USE_SFIO
94
06936a3c 95A "legacy" implementation in terms of the "sfio" library. Used for
96some specialist applications on Unix machines ("sfio" is not widely
97ported away from Unix). Most of above are #define'd to the sfio
98functions. PerlIO * is in this case Sfio_t *.
50b80e25 99
100=item 3. USE_PERLIO
101
06936a3c 102Introduced just after perl5.7.0, this is a re-implementation of the
103above abstraction which allows perl more control over how IO is done
104as it decouples IO from the way the operating system and C library
105choose to do things. For USE_PERLIO PerlIO * has an extra layer of
106indirection - it is a pointer-to-a-pointer. This allows the PerlIO *
210b36aa 107to remain with a known value while swapping the implementation around
06936a3c 108underneath I<at run time>. In this case all the above are true (but
109very simple) functions which call the underlying implementation.
50b80e25 110
06936a3c 111This is the only implementation for which C<PerlIO_apply_layers()>
112does anything "interesting".
50b80e25 113
114The USE_PERLIO implementation is described in L<perliol>.
115
116=back
117
06936a3c 118Because "perlio.h" is a thin layer (for efficiency) the semantics of
39ac7f1b 119these functions are somewhat dependent on the underlying implementation.
120Where these variations are understood they are noted below.
50b80e25 121
39ac7f1b 122Unless otherwise noted, functions return 0 on success, or a negative
123value (usually C<EOF> which is usually -1) and set C<errno> on error.
50b80e25 124
125=over 4
760ac839 126
127=item B<PerlIO_stdin()>, B<PerlIO_stdout()>, B<PerlIO_stderr()>
128
129Use these rather than C<stdin>, C<stdout>, C<stderr>. They are written
130to look like "function calls" rather than variables because this makes
54310121 131it easier to I<make them> function calls if platform cannot export data
132to loaded modules, or if (say) different "threads" might have different
760ac839 133values.
134
135=item B<PerlIO_open(path, mode)>, B<PerlIO_fdopen(fd,mode)>
136
3039a93d 137These correspond to fopen()/fdopen() and the arguments are the same.
06936a3c 138Return C<NULL> and set C<errno> if there is an error. There may be an
139implementation limit on the number of open handles, which may be lower
140than the limit on the number of open files - C<errno> may not be set
210b36aa 141when C<NULL> is returned if this limit is exceeded.
50b80e25 142
11e1c8f2 143=item B<PerlIO_reopen(path,mode,f)>
50b80e25 144
145While this currently exists in all three implementations perl itself
146does not use it. I<As perl does not use it, it is not well tested.>
147
06936a3c 148Perl prefers to C<dup> the new low-level descriptor to the descriptor
149used by the existing PerlIO. This may become the behaviour of this
150function in the future.
760ac839 151
152=item B<PerlIO_printf(f,fmt,...)>, B<PerlIO_vprintf(f,fmt,a)>
153
7b8d334a 154These are fprintf()/vfprintf() equivalents.
760ac839 155
156=item B<PerlIO_stdoutf(fmt,...)>
157
158This is printf() equivalent. printf is #defined to this function,
84dc3c4d 159so it is (currently) legal to use C<printf(fmt,...)> in perl sources.
760ac839 160
161=item B<PerlIO_read(f,buf,count)>, B<PerlIO_write(f,buf,count)>
162
06936a3c 163These correspond to fread() and fwrite(). Note that arguments are
164different, there is only one "count" and order has "file"
165first. Returns a byte count if successful (which may be zero), returns
166negative value and sets C<errno> on error. Depending on
167implementation C<errno> may be C<EINTR> if operation was interrupted
168by a signal.
760ac839 169
170=item B<PerlIO_close(f)>
171
06936a3c 172Depending on implementation C<errno> may be C<EINTR> if operation was
173interrupted by a signal.
50b80e25 174
21917246 175=item B<PerlIO_puts(f,s)>, B<PerlIO_putc(f,c)>
760ac839 176
54310121 177These correspond to fputs() and fputc().
760ac839 178Note that arguments have been revised to have "file" first.
179
21917246 180=item B<PerlIO_ungetc(f,c)>
760ac839 181
06936a3c 182This corresponds to ungetc(). Note that arguments have been revised
183to have "file" first. Arranges that next read operation will return
184the byte B<c>. Despite the implied "character" in the name only
185values in the range 0..0xFF are defined. Returns the byte B<c> on
186success or -1 (C<EOF>) on error. The number of bytes that can be
187"pushed back" may vary, only 1 character is certain, and then only if
188it is the last character that was read from the handle.
760ac839 189
190=item B<PerlIO_getc(f)>
191
192This corresponds to getc().
50b80e25 193Despite the c in the name only byte range 0..0xFF is supported.
3039a93d 194Returns the character read or -1 (C<EOF>) on error.
760ac839 195
196=item B<PerlIO_eof(f)>
197
06936a3c 198This corresponds to feof(). Returns a true/false indication of
199whether the handle is at end of file. For terminal devices this may
200or may not be "sticky" depending on the implementation. The flag is
201cleared by PerlIO_seek(), or PerlIO_rewind().
760ac839 202
203=item B<PerlIO_error(f)>
204
06936a3c 205This corresponds to ferror(). Returns a true/false indication of
206whether there has been an IO error on the handle.
760ac839 207
208=item B<PerlIO_fileno(f)>
209
06936a3c 210This corresponds to fileno(), note that on some platforms, the meaning
211of "fileno" may not match Unix. Returns -1 if the handle has no open
212descriptor associated with it.
760ac839 213
214=item B<PerlIO_clearerr(f)>
215
06936a3c 216This corresponds to clearerr(), i.e., clears 'error' and (usually)
217'eof' flags for the "stream". Does not return a value.
760ac839 218
219=item B<PerlIO_flush(f)>
220
06936a3c 221This corresponds to fflush(). Sends any buffered write data to the
222underlying file. If called with C<NULL> this may flush all open
223streams (or core dump). Calling on a handle open for read only, or on
224which last operation was a read of some kind may lead to undefined
225behaviour.
760ac839 226
50b80e25 227=item B<PerlIO_seek(f,offset,whence)>
760ac839 228
06936a3c 229This corresponds to fseek(). Sends buffered write data to the
230underlying file, or discards any buffered read data, then positions
231the file desciptor as specified by B<offset> and B<whence> (sic).
232This is the correct thing to do when switching between read and write
233on the same handle (see issues with PerlIO_flush() above). Offset is
234of type C<Off_t> which is a perl Configure value which may not be same
50b80e25 235as stdio's C<off_t>.
760ac839 236
50b80e25 237=item B<PerlIO_tell(f)>
760ac839 238
06936a3c 239This corresponds to ftell(). Returns the current file position, or
240(Off_t) -1 on error. May just return value system "knows" without
241making a system call or checking the underlying file descriptor (so
242use on shared file descriptors is not safe without a
243PerlIO_seek()). Return value is of type C<Off_t> which is a perl
244Configure value which may not be same as stdio's C<off_t>.
760ac839 245
246=item B<PerlIO_getpos(f,p)>, B<PerlIO_setpos(f,p)>
247
06936a3c 248These correspond (loosely) to fgetpos() and fsetpos(). Rather than
249stdio's Fpos_t they expect a "Perl Scalar Value" to be passed. What is
250stored there should be considered opaque. The layout of the data may
251vary from handle to handle. When not using stdio or if platform does
252not have the stdio calls then they are implemented in terms of
253PerlIO_tell() and PerlIO_seek().
760ac839 254
255=item B<PerlIO_rewind(f)>
256
50b80e25 257This corresponds to rewind(). It is usually defined as being
258
259 PerlIO_seek(f,(Off_t)0L, SEEK_SET);
260 PerlIO_clearerr(f);
261
760ac839 262=item B<PerlIO_tmpfile()>
263
06936a3c 264This corresponds to tmpfile(), i.e., returns an anonymous PerlIO or
265NULL on error. The system will attempt to automatically delete the
266file when closed. On Unix the file is usually C<unlink>-ed just after
267it is created so it does not matter how it gets closed. On other
268systems the file may only be deleted if closed via PerlIO_close()
269and/or the program exits via C<exit>. Depending on the implementation
270there may be "race conditions" which allow other processes access to
271the file, though in general it will be safer in this regard than
272ad. hoc. schemes.
50b80e25 273
274=item B<PerlIO_setlinebuf(f)>
275
06936a3c 276This corresponds to setlinebuf(). Does not return a value. What
277constitutes a "line" is implementation dependent but usually means
278that writing "\n" flushes the buffer. What happens with things like
279"this\nthat" is uncertain. (Perl core uses it I<only> when "dumping";
280it has nothing to do with $| auto-flush.)
760ac839 281
54310121 282=back
760ac839 283
510d21e9 284=head2 Co-existence with stdio
760ac839 285
510d21e9 286There is outline support for co-existence of PerlIO with stdio.
06936a3c 287Obviously if PerlIO is implemented in terms of stdio there is no
288problem. However in other cases then mechanisms must exist to create a
289FILE * which can be passed to library code which is going to use stdio
290calls.
50b80e25 291
210b36aa 292The first step is to add this line:
50b80e25 293
294 #define PERLIO_NOT_STDIO 0
295
06936a3c 296I<before> including any perl header files. (This will probably become
297the default at some point). That prevents "perlio.h" from attempting
298to #define stdio functions onto PerlIO functions.
50b80e25 299
06936a3c 300XS code is probably better using "typemap" if it expects FILE *
301arguments. The standard typemap will be adjusted to comprehend any
302changes in this area.
760ac839 303
304=over 4
305
306=item B<PerlIO_importFILE(f,flags)>
307
06936a3c 308Used to get a PerlIO * from a FILE *. May need additional arguments,
309interface under review.
760ac839 310
06936a3c 311The flags argument was meant to be used for read vs write vs
312read/write information. In hindsight it would have been better to make
313it a char *mode as in fopen/freopen.
50b80e25 314
760ac839 315=item B<PerlIO_exportFILE(f,flags)>
316
06936a3c 317Given a PerlIO * return a 'native' FILE * suitable for passing to code
318expecting to be compiled and linked with ANSI C I<stdio.h>.
760ac839 319
06936a3c 320The fact that such a FILE * has been 'exported' is recorded, and may
321affect future PerlIO operations on the original PerlIO *.
760ac839 322
323=item B<PerlIO_findFILE(f)>
324
06936a3c 325Returns previously 'exported' FILE * (if any). Placeholder until
326interface is fully defined.
760ac839 327
328=item B<PerlIO_releaseFILE(p,f)>
329
06936a3c 330Calling PerlIO_releaseFILE informs PerlIO that all use of FILE * is
331complete. It is removed from list of 'exported' FILE *s, and
332associated PerlIO * should revert to original behaviour.
760ac839 333
760ac839 334=back
335
50b80e25 336=head2 "Fast gets" Functions
337
06936a3c 338In addition to standard-like API defined so far above there is an
339"implementation" interface which allows perl to get at internals of
340PerlIO. The following calls correspond to the various FILE_xxx macros
341determined by Configure - or their equivalent in other
342implementations. This section is really of interest to only those
343concerned with detailed perl-core behaviour, implementing a PerlIO
344mapping or writing code which can make use of the "read ahead" that
345has been done by the IO system in the same way perl does. Note that
346any code that uses these interfaces must be prepared to do things the
347traditional way if a handle does not support them.
760ac839 348
349=over 4
350
50b80e25 351=item B<PerlIO_fast_gets(f)>
760ac839 352
50b80e25 353Returns true if implementation has all the interfaces required to
354allow perl's C<sv_gets> to "bypass" normal IO mechanism.
355This can vary from handle to handle.
760ac839 356
50b80e25 357 PerlIO_fast_gets(f) = PerlIO_has_cntptr(f) && \
358 PerlIO_canset_cnt(f) && \
359 `Can set pointer into buffer'
760ac839 360
760ac839 361
50b80e25 362=item B<PerlIO_has_cntptr(f)>
760ac839 363
06936a3c 364Implementation can return pointer to current position in the "buffer"
365and a count of bytes available in the buffer. Do not use this - use
366PerlIO_fast_gets.
760ac839 367
50b80e25 368=item B<PerlIO_get_cnt(f)>
760ac839 369
06936a3c 370Return count of readable bytes in the buffer. Zero or negative return
371means no more bytes available.
760ac839 372
50b80e25 373=item B<PerlIO_get_ptr(f)>
760ac839 374
06936a3c 375Return pointer to next readable byte in buffer, accessing via the
376pointer (dereferencing) is only safe if PerlIO_get_cnt() has returned
377a positive value. Only positive offsets up to value returned by
378PerlIO_get_cnt() are allowed.
760ac839 379
380=item B<PerlIO_set_ptrcnt(f,p,c)>
381
54310121 382Set pointer into buffer, and a count of bytes still in the
06936a3c 383buffer. Should be used only to set pointer to within range implied by
384previous calls to C<PerlIO_get_ptr> and C<PerlIO_get_cnt>. The two
385values I<must> be consistent with each other (implementation may only
386use one or the other or may require both).
50b80e25 387
388=item B<PerlIO_canset_cnt(f)>
389
390Implementation can adjust its idea of number of bytes in the buffer.
391Do not use this - use PerlIO_fast_gets.
760ac839 392
393=item B<PerlIO_set_cnt(f,c)>
394
06936a3c 395Obscure - set count of bytes in the buffer. Deprecated. Only usable
396if PerlIO_canset_cnt() returns true. Currently used in only doio.c to
397force count less than -1 to -1. Perhaps should be PerlIO_set_empty or
398similar. This call may actually do nothing if "count" is deduced from
399pointer and a "limit". Do not use this - use PerlIO_set_ptrcnt().
760ac839 400
401=item B<PerlIO_has_base(f)>
402
50b80e25 403Returns true if implementation has a buffer, and can return pointer
760ac839 404to whole buffer and its size. Used by perl for B<-T> / B<-B> tests.
405Other uses would be very obscure...
406
407=item B<PerlIO_get_base(f)>
408
50b80e25 409Return I<start> of buffer. Access only positive offsets in the buffer
410up to the value returned by PerlIO_get_bufsiz().
760ac839 411
412=item B<PerlIO_get_bufsiz(f)>
413
06936a3c 414Return the I<total number of bytes> in the buffer, this is neither the
415number that can be read, nor the amount of memory allocated to the
416buffer. Rather it is what the operating system and/or implementation
417happened to C<read()> (or whatever) last time IO was requested.
50b80e25 418
419=back
420
421=head2 Other Functions
422
423=over 4
424
425=item PerlIO_apply_layers(f,mode,layers)
426
427The new interface to the USE_PERLIO implementation. The layers ":crlf"
428and ":raw" are only ones allowed for other implementations and those
429are silently ignored. Use PerlIO_binmode() below for the portable
430case.
431
432=item PerlIO_binmode(f,ptype,imode,layers)
433
434The hook used by perl's C<binmode> operator.
210b36aa 435B<ptype> is perl's character for the kind of IO:
50b80e25 436
437=over 8
438
11e1c8f2 439=item 'E<lt>' read
50b80e25 440
11e1c8f2 441=item 'E<gt>' write
50b80e25 442
443=item '+' read/write
444
445=back
446
447B<imode> is C<O_BINARY> or C<O_TEXT>.
448
449B<layers> is a string of layers to apply, only ":raw" or :"crlf" make
450sense in the non USE_PERLIO case.
451
452Portable cases are:
453
454 PerlIO_binmode(f,ptype,O_BINARY,":raw");
455and
456 PerlIO_binmode(f,ptype,O_TEXT,":crlf");
457
06936a3c 458On Unix these calls probably have no effect whatsoever. Elsewhere
459they alter "\n" to CR,LF translation and possibly cause a special text
460"end of file" indicator to be written or honoured on read. The effect
461of making the call after doing any IO to the handle depends on the
462implementation. (It may be ignored, affect any data which is already
463buffered as well, or only apply to subsequent data.)
50b80e25 464
465=item PerlIO_debug(fmt,...)
466
06936a3c 467PerlIO_debug is a printf()-like function which can be used for
468debugging. No return value. Its main use is inside PerlIO where using
469real printf, warn() etc. would recursively call PerlIO and be a
470problem.
50b80e25 471
06936a3c 472PerlIO_debug writes to the file named by $ENV{'PERLIO_DEBUG'} typical
473use might be
50b80e25 474
ada498b9 475 Bourne shells (sh, ksh, bash, zsh, ash, ...):
50b80e25 476 PERLIO_DEBUG=/dev/tty ./perl somescript some args
477
ada498b9 478 Csh/Tcsh:
50b80e25 479 setenv PERLIO_DEBUG /dev/tty
480 ./perl somescript some args
481
ada498b9 482 If you have the "env" utility:
483 env PERLIO_DEBUG=/dev/tty ./perl somescript some args
484
50b80e25 485 Win32:
486 set PERLIO_DEBUG=CON
487 perl somescript some args
488
489If $ENV{'PERLIO_DEBUG'} is not set PerlIO_debug() is a no-op.
760ac839 490
54310121 491=back