1PERLAPIO(1) Perl Programmers Reference Guide PERLAPIO(1)
2
6 perlapio - perl's IO abstraction interface.
7
9 #define PERLIO_NOT_STDIO 0 /* For co-existence with stdio only */
10 #include <perlio.h> /* Usually via #include <perl.h> */
11 PerlIO *PerlIO_stdin(void);
13 PerlIO *PerlIO_stdout(void);
14 PerlIO *PerlIO_stderr(void);
15 PerlIO *PerlIO_open(const char *path,const char *mode);
17 PerlIO *PerlIO_fdopen(int fd, const char *mode);
18 PerlIO *PerlIO_reopen(const char *path, const char *mode, PerlIO *old); /* deprecated */
19 int PerlIO_close(PerlIO *f);
20 int PerlIO_stdoutf(const char *fmt,...)
22 int PerlIO_puts(PerlIO *f,const char *string);
23 int PerlIO_putc(PerlIO *f,int ch);
24 int PerlIO_write(PerlIO *f,const void *buf,size_t numbytes);
25 int PerlIO_printf(PerlIO *f, const char *fmt,...);
26 int PerlIO_vprintf(PerlIO *f, const char *fmt, va_list args);
27 int PerlIO_flush(PerlIO *f);
28 int PerlIO_eof(PerlIO *f);
30 int PerlIO_error(PerlIO *f);
31 void PerlIO_clearerr(PerlIO *f);
32 int PerlIO_getc(PerlIO *d);
34 int PerlIO_ungetc(PerlIO *f,int ch);
35 int PerlIO_read(PerlIO *f, void *buf, size_t numbytes);
36 int PerlIO_fileno(PerlIO *f);
38 void PerlIO_setlinebuf(PerlIO *f);
40 Off_t PerlIO_tell(PerlIO *f);
42 int PerlIO_seek(PerlIO *f, Off_t offset, int whence);
43 void PerlIO_rewind(PerlIO *f);
44 int PerlIO_getpos(PerlIO *f, SV *save); /* prototype changed */
46 int PerlIO_setpos(PerlIO *f, SV *saved); /* prototype changed */
47 int PerlIO_fast_gets(PerlIO *f);
49 int PerlIO_has_cntptr(PerlIO *f);
50 int PerlIO_get_cnt(PerlIO *f);
51 char *PerlIO_get_ptr(PerlIO *f);
52 void PerlIO_set_ptrcnt(PerlIO *f, char *ptr, int count);
53 int PerlIO_canset_cnt(PerlIO *f); /* deprecated */
55 void PerlIO_set_cnt(PerlIO *f, int count); /* deprecated */
56 int PerlIO_has_base(PerlIO *f);
58 char *PerlIO_get_base(PerlIO *f);
59 int PerlIO_get_bufsiz(PerlIO *f);
60 PerlIO *PerlIO_importFILE(FILE *stdio, const char *mode);
62 FILE *PerlIO_exportFILE(PerlIO *f, int flags);
63 FILE *PerlIO_findFILE(PerlIO *f);
64 void PerlIO_releaseFILE(PerlIO *f,FILE *stdio);
65 int PerlIO_apply_layers(PerlIO *f, const char *mode, const char *layers);
67 int PerlIO_binmode(PerlIO *f, int ptype, int imode, const char *layers);
68 void PerlIO_debug(const char *fmt,...)
69
71 Perl's source code, and extensions that want maximum portability,
72 should use the above functions instead of those defined in ANSI C's
73 stdio.h. The perl headers (in particular "perlio.h") will "#define"
74 them to the I/O mechanism selected at Configure time.
75 The functions are modeled on those in stdio.h, but parameter order has
77 been "tidied up a little".
78 "PerlIO *" takes the place of FILE *. Like FILE * it should be treated
80 as opaque (it is probably safe to assume it is a pointer to something).
81 There are currently three implementations:
83 1. USE_STDIO
85 All above are #define'd to stdio functions or are trivial wrapper
86 functions which call stdio. In this case only PerlIO * is a FILE *.
87 This has been the default implementation since the abstraction was
88 introduced in perl5.003_02.
89 2. USE_SFIO
91 A "legacy" implementation in terms of the "sfio" library. Used for
92 some specialist applications on Unix machines ("sfio" is not widely
93 ported away from Unix). Most of above are #define'd to the sfio
94 functions. PerlIO * is in this case Sfio_t *.
95 3. USE_PERLIO
97 Introduced just after perl5.7.0, this is a re-implementation of the
98 above abstraction which allows perl more control over how IO is
99 done as it decouples IO from the way the operating system and C
100 library choose to do things. For USE_PERLIO PerlIO * has an extra
101 layer of indirection - it is a pointer-to-a-pointer. This allows
102 the PerlIO * to remain with a known value while swapping the
103 implementation around underneath at run time. In this case all the
104 above are true (but very simple) functions which call the
105 underlying implementation.
106 This is the only implementation for which "PerlIO_apply_layers()"
108 does anything "interesting".
109 The USE_PERLIO implementation is described in perliol.
111 Because "perlio.h" is a thin layer (for efficiency) the semantics of
113 these functions are somewhat dependent on the underlying
114 implementation. Where these variations are understood they are noted
115 below.
116 Unless otherwise noted, functions return 0 on success, or a negative
118 value (usually "EOF" which is usually -1) and set "errno" on error.
119 PerlIO_stdin(), PerlIO_stdout(), PerlIO_stderr()
121 Use these rather than "stdin", "stdout", "stderr". They are written
122 to look like "function calls" rather than variables because this
123 makes it easier to make them function calls if platform cannot
124 export data to loaded modules, or if (say) different "threads"
125 might have different values.
126 PerlIO_open(path, mode), PerlIO_fdopen(fd,mode)
128 These correspond to fopen()/fdopen() and the arguments are the
129 same. Return "NULL" and set "errno" if there is an error. There
130 may be an implementation limit on the number of open handles, which
131 may be lower than the limit on the number of open files - "errno"
132 may not be set when "NULL" is returned if this limit is exceeded.
133 PerlIO_reopen(path,mode,f)
135 While this currently exists in all three implementations perl
136 itself does not use it. As perl does not use it, it is not well
137 tested.
138 Perl prefers to "dup" the new low-level descriptor to the
140 descriptor used by the existing PerlIO. This may become the
141 behaviour of this function in the future.
142 PerlIO_printf(f,fmt,...), PerlIO_vprintf(f,fmt,a)
144 These are fprintf()/vfprintf() equivalents.
145 PerlIO_stdoutf(fmt,...)
147 This is printf() equivalent. printf is #defined to this function,
148 so it is (currently) legal to use "printf(fmt,...)" in perl
149 sources.
150 PerlIO_read(f,buf,count), PerlIO_write(f,buf,count)
152 These correspond functionally to fread() and fwrite() but the
153 arguments and return values are different. The PerlIO_read() and
154 PerlIO_write() signatures have been modeled on the more sane low
155 level read() and write() functions instead: The "file" argument is
156 passed first, there is only one "count", and the return value can
157 distinguish between error and "EOF".
158 Returns a byte count if successful (which may be zero or positive),
160 returns negative value and sets "errno" on error. Depending on
161 implementation "errno" may be "EINTR" if operation was interrupted
162 by a signal.
163 PerlIO_close(f)
165 Depending on implementation "errno" may be "EINTR" if operation was
166 interrupted by a signal.
167 PerlIO_puts(f,s), PerlIO_putc(f,c)
169 These correspond to fputs() and fputc(). Note that arguments have
170 been revised to have "file" first.
171 PerlIO_ungetc(f,c)
173 This corresponds to ungetc(). Note that arguments have been
174 revised to have "file" first. Arranges that next read operation
175 will return the byte c. Despite the implied "character" in the
176 name only values in the range 0..0xFF are defined. Returns the byte
177 c on success or -1 ("EOF") on error. The number of bytes that can
178 be "pushed back" may vary, only 1 character is certain, and then
179 only if it is the last character that was read from the handle.
180 PerlIO_getc(f)
182 This corresponds to getc(). Despite the c in the name only byte
183 range 0..0xFF is supported. Returns the character read or -1
184 ("EOF") on error.
185 PerlIO_eof(f)
187 This corresponds to feof(). Returns a true/false indication of
188 whether the handle is at end of file. For terminal devices this
189 may or may not be "sticky" depending on the implementation. The
190 flag is cleared by PerlIO_seek(), or PerlIO_rewind().
191 PerlIO_error(f)
193 This corresponds to ferror(). Returns a true/false indication of
194 whether there has been an IO error on the handle.
195 PerlIO_fileno(f)
197 This corresponds to fileno(), note that on some platforms, the
198 meaning of "fileno" may not match Unix. Returns -1 if the handle
199 has no open descriptor associated with it.
200 PerlIO_clearerr(f)
202 This corresponds to clearerr(), i.e., clears 'error' and (usually)
203 'eof' flags for the "stream". Does not return a value.
204 PerlIO_flush(f)
206 This corresponds to fflush(). Sends any buffered write data to the
207 underlying file. If called with "NULL" this may flush all open
208 streams (or core dump with some USE_STDIO implementations).
209 Calling on a handle open for read only, or on which last operation
210 was a read of some kind may lead to undefined behaviour on some
211 USE_STDIO implementations. The USE_PERLIO (layers) implementation
212 tries to behave better: it flushes all open streams when passed
213 "NULL", and attempts to retain data on read streams either in the
214 buffer or by seeking the handle to the current logical position.
215 PerlIO_seek(f,offset,whence)
217 This corresponds to fseek(). Sends buffered write data to the
218 underlying file, or discards any buffered read data, then positions
219 the file descriptor as specified by offset and whence (sic). This
220 is the correct thing to do when switching between read and write on
221 the same handle (see issues with PerlIO_flush() above). Offset is
222 of type "Off_t" which is a perl Configure value which may not be
223 same as stdio's "off_t".
224 PerlIO_tell(f)
226 This corresponds to ftell(). Returns the current file position, or
227 (Off_t) -1 on error. May just return value system "knows" without
228 making a system call or checking the underlying file descriptor (so
229 use on shared file descriptors is not safe without a
230 PerlIO_seek()). Return value is of type "Off_t" which is a perl
231 Configure value which may not be same as stdio's "off_t".
232 PerlIO_getpos(f,p), PerlIO_setpos(f,p)
234 These correspond (loosely) to fgetpos() and fsetpos(). Rather than
235 stdio's Fpos_t they expect a "Perl Scalar Value" to be passed. What
236 is stored there should be considered opaque. The layout of the data
237 may vary from handle to handle. When not using stdio or if
238 platform does not have the stdio calls then they are implemented in
239 terms of PerlIO_tell() and PerlIO_seek().
240 PerlIO_rewind(f)
242 This corresponds to rewind(). It is usually defined as being
243 PerlIO_seek(f,(Off_t)0L, SEEK_SET);
245 PerlIO_clearerr(f);
246 PerlIO_tmpfile()
248 This corresponds to tmpfile(), i.e., returns an anonymous PerlIO or
249 NULL on error. The system will attempt to automatically delete the
250 file when closed. On Unix the file is usually "unlink"-ed just
251 after it is created so it does not matter how it gets closed. On
252 other systems the file may only be deleted if closed via
253 PerlIO_close() and/or the program exits via "exit". Depending on
254 the implementation there may be "race conditions" which allow other
255 processes access to the file, though in general it will be safer in
256 this regard than ad. hoc. schemes.
257 PerlIO_setlinebuf(f)
259 This corresponds to setlinebuf(). Does not return a value. What
260 constitutes a "line" is implementation dependent but usually means
261 that writing "\n" flushes the buffer. What happens with things
262 like "this\nthat" is uncertain. (Perl core uses it only when
263 "dumping"; it has nothing to do with $| auto-flush.)
264 Co-existence with stdio
266 There is outline support for co-existence of PerlIO with stdio.
267 Obviously if PerlIO is implemented in terms of stdio there is no
268 problem. However in other cases then mechanisms must exist to create a
269 FILE * which can be passed to library code which is going to use stdio
270 calls.
271 The first step is to add this line:
273 #define PERLIO_NOT_STDIO 0
275 before including any perl header files. (This will probably become the
277 default at some point). That prevents "perlio.h" from attempting to
278 #define stdio functions onto PerlIO functions.
279 XS code is probably better using "typemap" if it expects FILE *
281 arguments. The standard typemap will be adjusted to comprehend any
282 changes in this area.
283 PerlIO_importFILE(f,mode)
285 Used to get a PerlIO * from a FILE *.
286 The mode argument should be a string as would be passed to
288 fopen/PerlIO_open. If it is NULL then - for legacy support - the
289 code will (depending upon the platform and the implementation)
290 either attempt to empirically determine the mode in which f is
291 open, or use "r+" to indicate a read/write stream.
292 Once called the FILE * should ONLY be closed by calling
294 "PerlIO_close()" on the returned PerlIO *.
295 The PerlIO is set to textmode. Use PerlIO_binmode if this is not
297 the desired mode.
298 This is not the reverse of PerlIO_exportFILE().
300 PerlIO_exportFILE(f,mode)
302 Given a PerlIO * create a 'native' FILE * suitable for passing to
303 code expecting to be compiled and linked with ANSI C stdio.h. The
304 mode argument should be a string as would be passed to
305 fopen/PerlIO_open. If it is NULL then - for legacy support - the
306 FILE * is opened in same mode as the PerlIO *.
307 The fact that such a FILE * has been 'exported' is recorded,
309 (normally by pushing a new :stdio "layer" onto the PerlIO *), which
310 may affect future PerlIO operations on the original PerlIO *. You
311 should not call "fclose()" on the file unless you call
312 "PerlIO_releaseFILE()" to disassociate it from the PerlIO *. (Do
313 not use PerlIO_importFILE() for doing the disassociation.)
314 Calling this function repeatedly will create a FILE * on each call
316 (and will push an :stdio layer each time as well).
317 PerlIO_releaseFILE(p,f)
319 Calling PerlIO_releaseFILE informs PerlIO that all use of FILE * is
320 complete. It is removed from the list of 'exported' FILE *s, and
321 the associated PerlIO * should revert to its original behaviour.
322 Use this to disassociate a file from a PerlIO * that was associated
324 using PerlIO_exportFILE().
325 PerlIO_findFILE(f)
327 Returns a native FILE * used by a stdio layer. If there is none, it
328 will create one with PerlIO_exportFILE. In either case the FILE *
329 should be considered as belonging to PerlIO subsystem and should
330 only be closed by calling "PerlIO_close()".
331 "Fast gets" Functions
333 In addition to standard-like API defined so far above there is an
334 "implementation" interface which allows perl to get at internals of
335 PerlIO. The following calls correspond to the various FILE_xxx macros
336 determined by Configure - or their equivalent in other implementations.
337 This section is really of interest to only those concerned with
338 detailed perl-core behaviour, implementing a PerlIO mapping or writing
339 code which can make use of the "read ahead" that has been done by the
340 IO system in the same way perl does. Note that any code that uses these
341 interfaces must be prepared to do things the traditional way if a
342 handle does not support them.
343 PerlIO_fast_gets(f)
345 Returns true if implementation has all the interfaces required to
346 allow perl's "sv_gets" to "bypass" normal IO mechanism. This can
347 vary from handle to handle.
348 PerlIO_fast_gets(f) = PerlIO_has_cntptr(f) && \
350 PerlIO_canset_cnt(f) && \
351 `Can set pointer into buffer'
352 PerlIO_has_cntptr(f)
354 Implementation can return pointer to current position in the
355 "buffer" and a count of bytes available in the buffer. Do not use
356 this - use PerlIO_fast_gets.
357 PerlIO_get_cnt(f)
359 Return count of readable bytes in the buffer. Zero or negative
360 return means no more bytes available.
361 PerlIO_get_ptr(f)
363 Return pointer to next readable byte in buffer, accessing via the
364 pointer (dereferencing) is only safe if PerlIO_get_cnt() has
365 returned a positive value. Only positive offsets up to value
366 returned by PerlIO_get_cnt() are allowed.
367 PerlIO_set_ptrcnt(f,p,c)
369 Set pointer into buffer, and a count of bytes still in the buffer.
370 Should be used only to set pointer to within range implied by
371 previous calls to "PerlIO_get_ptr" and "PerlIO_get_cnt". The two
372 values must be consistent with each other (implementation may only
373 use one or the other or may require both).
374 PerlIO_canset_cnt(f)
376 Implementation can adjust its idea of number of bytes in the
377 buffer. Do not use this - use PerlIO_fast_gets.
378 PerlIO_set_cnt(f,c)
380 Obscure - set count of bytes in the buffer. Deprecated. Only
381 usable if PerlIO_canset_cnt() returns true. Currently used in only
382 doio.c to force count less than -1 to -1. Perhaps should be
383 PerlIO_set_empty or similar. This call may actually do nothing if
384 "count" is deduced from pointer and a "limit". Do not use this -
385 use PerlIO_set_ptrcnt().
386 PerlIO_has_base(f)
388 Returns true if implementation has a buffer, and can return pointer
389 to whole buffer and its size. Used by perl for -T / -B tests.
390 Other uses would be very obscure...
391 PerlIO_get_base(f)
393 Return start of buffer. Access only positive offsets in the buffer
394 up to the value returned by PerlIO_get_bufsiz().
395 PerlIO_get_bufsiz(f)
397 Return the total number of bytes in the buffer, this is neither the
398 number that can be read, nor the amount of memory allocated to the
399 buffer. Rather it is what the operating system and/or
400 implementation happened to "read()" (or whatever) last time IO was
401 requested.
402 Other Functions
404 PerlIO_apply_layers(f,mode,layers)
405 The new interface to the USE_PERLIO implementation. The layers
406 ":crlf" and ":raw" are only ones allowed for other implementations
407 and those are silently ignored. (As of perl5.8 ":raw" is
408 deprecated.) Use PerlIO_binmode() below for the portable case.
409 PerlIO_binmode(f,ptype,imode,layers)
411 The hook used by perl's "binmode" operator. ptype is perl's
412 character for the kind of IO:
413 '<' read
415 '>' write
416 '+' read/write
417 imode is "O_BINARY" or "O_TEXT".
419 layers is a string of layers to apply, only ":crlf" makes sense in
421 the non USE_PERLIO case. (As of perl5.8 ":raw" is deprecated in
422 favour of passing NULL.)
423 Portable cases are:
425 PerlIO_binmode(f,ptype,O_BINARY,NULL);
427 and
428 PerlIO_binmode(f,ptype,O_TEXT,":crlf");
429 On Unix these calls probably have no effect whatsoever. Elsewhere
431 they alter "\n" to CR,LF translation and possibly cause a special
432 text "end of file" indicator to be written or honoured on read. The
433 effect of making the call after doing any IO to the handle depends
434 on the implementation. (It may be ignored, affect any data which is
435 already buffered as well, or only apply to subsequent data.)
436 PerlIO_debug(fmt,...)
438 PerlIO_debug is a printf()-like function which can be used for
439 debugging. No return value. Its main use is inside PerlIO where
440 using real printf, warn() etc. would recursively call PerlIO and be
441 a problem.
442 PerlIO_debug writes to the file named by $ENV{'PERLIO_DEBUG'}
444 typical use might be
445 Bourne shells (sh, ksh, bash, zsh, ash, ...):
447 PERLIO_DEBUG=/dev/tty ./perl somescript some args
448 Csh/Tcsh:
450 setenv PERLIO_DEBUG /dev/tty
451 ./perl somescript some args
452 If you have the "env" utility:
454 env PERLIO_DEBUG=/dev/tty ./perl somescript some args
455 Win32:
457 set PERLIO_DEBUG=CON
458 perl somescript some args
459 If $ENV{'PERLIO_DEBUG'} is not set PerlIO_debug() is a no-op.
461perl v5.12.4 2011-06-01 PERLAPIO(1)