extra code in pp_concat, Take 2
[p5sagit/p5-mst-13.2.git] / pod / perlapio.pod
CommitLineData
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
4b069b44 59 PerlIO *PerlIO_importFILE(FILE *stdio, const char *mode);
50b80e25 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
2c2cb412 163These correspond functionally to fread() and fwrite() but the
164arguments and return values are different. The PerlIO_read() and
165PerlIO_write() signatures have been modeled on the more sane low level
166read() and write() functions instead: The "file" argument is passed
167first, there is only one "count", and the return value can distinguish
168between error and C<EOF>.
169
170Returns a byte count if successful (which may be zero or
c0a503cc 171positive), returns negative value and sets C<errno> on error.
172Depending on implementation C<errno> may be C<EINTR> if operation was
173interrupted by a signal.
760ac839 174
175=item B<PerlIO_close(f)>
176
06936a3c 177Depending on implementation C<errno> may be C<EINTR> if operation was
178interrupted by a signal.
50b80e25 179
21917246 180=item B<PerlIO_puts(f,s)>, B<PerlIO_putc(f,c)>
760ac839 181
54310121 182These correspond to fputs() and fputc().
760ac839 183Note that arguments have been revised to have "file" first.
184
21917246 185=item B<PerlIO_ungetc(f,c)>
760ac839 186
06936a3c 187This corresponds to ungetc(). Note that arguments have been revised
188to have "file" first. Arranges that next read operation will return
189the byte B<c>. Despite the implied "character" in the name only
190values in the range 0..0xFF are defined. Returns the byte B<c> on
191success or -1 (C<EOF>) on error. The number of bytes that can be
192"pushed back" may vary, only 1 character is certain, and then only if
193it is the last character that was read from the handle.
760ac839 194
195=item B<PerlIO_getc(f)>
196
197This corresponds to getc().
50b80e25 198Despite the c in the name only byte range 0..0xFF is supported.
3039a93d 199Returns the character read or -1 (C<EOF>) on error.
760ac839 200
201=item B<PerlIO_eof(f)>
202
06936a3c 203This corresponds to feof(). Returns a true/false indication of
204whether the handle is at end of file. For terminal devices this may
205or may not be "sticky" depending on the implementation. The flag is
206cleared by PerlIO_seek(), or PerlIO_rewind().
760ac839 207
208=item B<PerlIO_error(f)>
209
06936a3c 210This corresponds to ferror(). Returns a true/false indication of
211whether there has been an IO error on the handle.
760ac839 212
213=item B<PerlIO_fileno(f)>
214
06936a3c 215This corresponds to fileno(), note that on some platforms, the meaning
216of "fileno" may not match Unix. Returns -1 if the handle has no open
217descriptor associated with it.
760ac839 218
219=item B<PerlIO_clearerr(f)>
220
06936a3c 221This corresponds to clearerr(), i.e., clears 'error' and (usually)
222'eof' flags for the "stream". Does not return a value.
760ac839 223
224=item B<PerlIO_flush(f)>
225
06936a3c 226This corresponds to fflush(). Sends any buffered write data to the
227underlying file. If called with C<NULL> this may flush all open
fa11829f 228streams (or core dump with some USE_STDIO implementations). Calling
c0a503cc 229on a handle open for read only, or on which last operation was a read
230of some kind may lead to undefined behaviour on some USE_STDIO
231implementations. The USE_PERLIO (layers) implementation tries to
232behave better: it flushes all open streams when passed C<NULL>, and
233attempts to retain data on read streams either in the buffer or by
234seeking the handle to the current logical position.
760ac839 235
50b80e25 236=item B<PerlIO_seek(f,offset,whence)>
760ac839 237
06936a3c 238This corresponds to fseek(). Sends buffered write data to the
239underlying file, or discards any buffered read data, then positions
240the file desciptor as specified by B<offset> and B<whence> (sic).
241This is the correct thing to do when switching between read and write
242on the same handle (see issues with PerlIO_flush() above). Offset is
243of type C<Off_t> which is a perl Configure value which may not be same
50b80e25 244as stdio's C<off_t>.
760ac839 245
50b80e25 246=item B<PerlIO_tell(f)>
760ac839 247
06936a3c 248This corresponds to ftell(). Returns the current file position, or
249(Off_t) -1 on error. May just return value system "knows" without
250making a system call or checking the underlying file descriptor (so
251use on shared file descriptors is not safe without a
252PerlIO_seek()). Return value is of type C<Off_t> which is a perl
253Configure value which may not be same as stdio's C<off_t>.
760ac839 254
255=item B<PerlIO_getpos(f,p)>, B<PerlIO_setpos(f,p)>
256
06936a3c 257These correspond (loosely) to fgetpos() and fsetpos(). Rather than
258stdio's Fpos_t they expect a "Perl Scalar Value" to be passed. What is
259stored there should be considered opaque. The layout of the data may
260vary from handle to handle. When not using stdio or if platform does
261not have the stdio calls then they are implemented in terms of
262PerlIO_tell() and PerlIO_seek().
760ac839 263
264=item B<PerlIO_rewind(f)>
265
50b80e25 266This corresponds to rewind(). It is usually defined as being
267
268 PerlIO_seek(f,(Off_t)0L, SEEK_SET);
269 PerlIO_clearerr(f);
270
760ac839 271=item B<PerlIO_tmpfile()>
272
06936a3c 273This corresponds to tmpfile(), i.e., returns an anonymous PerlIO or
274NULL on error. The system will attempt to automatically delete the
275file when closed. On Unix the file is usually C<unlink>-ed just after
276it is created so it does not matter how it gets closed. On other
277systems the file may only be deleted if closed via PerlIO_close()
278and/or the program exits via C<exit>. Depending on the implementation
279there may be "race conditions" which allow other processes access to
280the file, though in general it will be safer in this regard than
281ad. hoc. schemes.
50b80e25 282
283=item B<PerlIO_setlinebuf(f)>
284
06936a3c 285This corresponds to setlinebuf(). Does not return a value. What
286constitutes a "line" is implementation dependent but usually means
287that writing "\n" flushes the buffer. What happens with things like
288"this\nthat" is uncertain. (Perl core uses it I<only> when "dumping";
289it has nothing to do with $| auto-flush.)
760ac839 290
54310121 291=back
760ac839 292
510d21e9 293=head2 Co-existence with stdio
760ac839 294
510d21e9 295There is outline support for co-existence of PerlIO with stdio.
06936a3c 296Obviously if PerlIO is implemented in terms of stdio there is no
297problem. However in other cases then mechanisms must exist to create a
298FILE * which can be passed to library code which is going to use stdio
299calls.
50b80e25 300
210b36aa 301The first step is to add this line:
50b80e25 302
303 #define PERLIO_NOT_STDIO 0
304
06936a3c 305I<before> including any perl header files. (This will probably become
306the default at some point). That prevents "perlio.h" from attempting
307to #define stdio functions onto PerlIO functions.
50b80e25 308
06936a3c 309XS code is probably better using "typemap" if it expects FILE *
310arguments. The standard typemap will be adjusted to comprehend any
311changes in this area.
760ac839 312
313=over 4
314
4b069b44 315=item B<PerlIO_importFILE(f,mode)>
760ac839 316
22569500 317Used to get a PerlIO * from a FILE *.
760ac839 318
c0a503cc 319The mode argument should be a string as would be passed to
320fopen/PerlIO_open. If it is NULL then - for legacy support - the code
321will (depending upon the platform and the implementation) either
322attempt to empirically determine the mode in which I<f> is open, or
323use "r+" to indicate a read/write stream.
22569500 324
325Once called the FILE * should I<ONLY> be closed by calling
326C<PerlIO_close()> on the returned PerlIO *.
327
f504ae08 328The PerlIO is set to textmode. Use PerlIO_binmode if this is
329not the desired mode.
330
b9d6bf13 331This is B<not> the reverse of PerlIO_exportFILE().
332
4b069b44 333=item B<PerlIO_exportFILE(f,mode)>
760ac839 334
8dcb5783 335Given a PerlIO * create a 'native' FILE * suitable for passing to code
c0a503cc 336expecting to be compiled and linked with ANSI C I<stdio.h>. The mode
337argument should be a string as would be passed to fopen/PerlIO_open.
338If it is NULL then - for legacy support - the FILE * is opened in same
339mode as the PerlIO *.
340
341The fact that such a FILE * has been 'exported' is recorded, (normally
342by pushing a new :stdio "layer" onto the PerlIO *), which may affect
343future PerlIO operations on the original PerlIO *. You should not
344call C<fclose()> on the file unless you call C<PerlIO_releaseFILE()>
345to disassociate it from the PerlIO *. (Do not use PerlIO_importFILE()
346for doing the disassociation.)
760ac839 347
22569500 348Calling this function repeatedly will create a FILE * on each call
349(and will push an :stdio layer each time as well).
760ac839 350
351=item B<PerlIO_releaseFILE(p,f)>
352
06936a3c 353Calling PerlIO_releaseFILE informs PerlIO that all use of FILE * is
65dabbe3 354complete. It is removed from the list of 'exported' FILE *s, and the
355associated PerlIO * should revert to its original behaviour.
760ac839 356
b9d6bf13 357Use this to disassociate a file from a PerlIO * that was associated
358using PerlIO_exportFILE().
359
22569500 360=item B<PerlIO_findFILE(f)>
361
362Returns a native FILE * used by a stdio layer. If there is none, it
363will create one with PerlIO_exportFILE. In either case the FILE *
65dabbe3 364should be considered as belonging to PerlIO subsystem and should
22569500 365only be closed by calling C<PerlIO_close()>.
366
8dcb5783 367
760ac839 368=back
369
50b80e25 370=head2 "Fast gets" Functions
371
06936a3c 372In addition to standard-like API defined so far above there is an
373"implementation" interface which allows perl to get at internals of
374PerlIO. The following calls correspond to the various FILE_xxx macros
375determined by Configure - or their equivalent in other
376implementations. This section is really of interest to only those
377concerned with detailed perl-core behaviour, implementing a PerlIO
378mapping or writing code which can make use of the "read ahead" that
379has been done by the IO system in the same way perl does. Note that
380any code that uses these interfaces must be prepared to do things the
381traditional way if a handle does not support them.
760ac839 382
383=over 4
384
50b80e25 385=item B<PerlIO_fast_gets(f)>
760ac839 386
50b80e25 387Returns true if implementation has all the interfaces required to
c0a503cc 388allow perl's C<sv_gets> to "bypass" normal IO mechanism. This can
389vary from handle to handle.
760ac839 390
50b80e25 391 PerlIO_fast_gets(f) = PerlIO_has_cntptr(f) && \
392 PerlIO_canset_cnt(f) && \
393 `Can set pointer into buffer'
760ac839 394
760ac839 395
50b80e25 396=item B<PerlIO_has_cntptr(f)>
760ac839 397
06936a3c 398Implementation can return pointer to current position in the "buffer"
399and a count of bytes available in the buffer. Do not use this - use
400PerlIO_fast_gets.
760ac839 401
50b80e25 402=item B<PerlIO_get_cnt(f)>
760ac839 403
06936a3c 404Return count of readable bytes in the buffer. Zero or negative return
405means no more bytes available.
760ac839 406
50b80e25 407=item B<PerlIO_get_ptr(f)>
760ac839 408
06936a3c 409Return pointer to next readable byte in buffer, accessing via the
410pointer (dereferencing) is only safe if PerlIO_get_cnt() has returned
411a positive value. Only positive offsets up to value returned by
412PerlIO_get_cnt() are allowed.
760ac839 413
414=item B<PerlIO_set_ptrcnt(f,p,c)>
415
54310121 416Set pointer into buffer, and a count of bytes still in the
06936a3c 417buffer. Should be used only to set pointer to within range implied by
418previous calls to C<PerlIO_get_ptr> and C<PerlIO_get_cnt>. The two
419values I<must> be consistent with each other (implementation may only
420use one or the other or may require both).
50b80e25 421
422=item B<PerlIO_canset_cnt(f)>
423
424Implementation can adjust its idea of number of bytes in the buffer.
425Do not use this - use PerlIO_fast_gets.
760ac839 426
427=item B<PerlIO_set_cnt(f,c)>
428
06936a3c 429Obscure - set count of bytes in the buffer. Deprecated. Only usable
430if PerlIO_canset_cnt() returns true. Currently used in only doio.c to
431force count less than -1 to -1. Perhaps should be PerlIO_set_empty or
432similar. This call may actually do nothing if "count" is deduced from
433pointer and a "limit". Do not use this - use PerlIO_set_ptrcnt().
760ac839 434
435=item B<PerlIO_has_base(f)>
436
50b80e25 437Returns true if implementation has a buffer, and can return pointer
760ac839 438to whole buffer and its size. Used by perl for B<-T> / B<-B> tests.
439Other uses would be very obscure...
440
441=item B<PerlIO_get_base(f)>
442
50b80e25 443Return I<start> of buffer. Access only positive offsets in the buffer
444up to the value returned by PerlIO_get_bufsiz().
760ac839 445
446=item B<PerlIO_get_bufsiz(f)>
447
06936a3c 448Return the I<total number of bytes> in the buffer, this is neither the
449number that can be read, nor the amount of memory allocated to the
450buffer. Rather it is what the operating system and/or implementation
451happened to C<read()> (or whatever) last time IO was requested.
50b80e25 452
453=back
454
455=head2 Other Functions
456
457=over 4
458
459=item PerlIO_apply_layers(f,mode,layers)
460
461The new interface to the USE_PERLIO implementation. The layers ":crlf"
462and ":raw" are only ones allowed for other implementations and those
c0a503cc 463are silently ignored. (As of perl5.8 ":raw" is deprecated.) Use
464PerlIO_binmode() below for the portable case.
50b80e25 465
466=item PerlIO_binmode(f,ptype,imode,layers)
467
468The hook used by perl's C<binmode> operator.
210b36aa 469B<ptype> is perl's character for the kind of IO:
50b80e25 470
471=over 8
472
11e1c8f2 473=item 'E<lt>' read
50b80e25 474
11e1c8f2 475=item 'E<gt>' write
50b80e25 476
477=item '+' read/write
478
479=back
480
481B<imode> is C<O_BINARY> or C<O_TEXT>.
482
c0a503cc 483B<layers> is a string of layers to apply, only ":crlf" makes sense in
484the non USE_PERLIO case. (As of perl5.8 ":raw" is deprecated in favour
485of passing NULL.)
50b80e25 486
487Portable cases are:
488
4b069b44 489 PerlIO_binmode(f,ptype,O_BINARY,Nullch);
50b80e25 490and
491 PerlIO_binmode(f,ptype,O_TEXT,":crlf");
492
06936a3c 493On Unix these calls probably have no effect whatsoever. Elsewhere
494they alter "\n" to CR,LF translation and possibly cause a special text
495"end of file" indicator to be written or honoured on read. The effect
496of making the call after doing any IO to the handle depends on the
497implementation. (It may be ignored, affect any data which is already
498buffered as well, or only apply to subsequent data.)
50b80e25 499
500=item PerlIO_debug(fmt,...)
501
06936a3c 502PerlIO_debug is a printf()-like function which can be used for
503debugging. No return value. Its main use is inside PerlIO where using
504real printf, warn() etc. would recursively call PerlIO and be a
505problem.
50b80e25 506
06936a3c 507PerlIO_debug writes to the file named by $ENV{'PERLIO_DEBUG'} typical
508use might be
50b80e25 509
ada498b9 510 Bourne shells (sh, ksh, bash, zsh, ash, ...):
50b80e25 511 PERLIO_DEBUG=/dev/tty ./perl somescript some args
512
ada498b9 513 Csh/Tcsh:
50b80e25 514 setenv PERLIO_DEBUG /dev/tty
515 ./perl somescript some args
516
ada498b9 517 If you have the "env" utility:
518 env PERLIO_DEBUG=/dev/tty ./perl somescript some args
519
50b80e25 520 Win32:
521 set PERLIO_DEBUG=CON
522 perl somescript some args
523
524If $ENV{'PERLIO_DEBUG'} is not set PerlIO_debug() is a no-op.
760ac839 525
54310121 526=back