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, /* deprecated */
19 const char *mode, PerlIO *old);
20 int PerlIO_close(PerlIO *f);
21 int PerlIO_stdoutf(const char *fmt,...)
23 int PerlIO_puts(PerlIO *f,const char *string);
24 int PerlIO_putc(PerlIO *f,int ch);
25 SSize_t PerlIO_write(PerlIO *f,const void *buf,size_t numbytes);
26 int PerlIO_printf(PerlIO *f, const char *fmt,...);
27 int PerlIO_vprintf(PerlIO *f, const char *fmt, va_list args);
28 int PerlIO_flush(PerlIO *f);
29 int PerlIO_eof(PerlIO *f);
31 int PerlIO_error(PerlIO *f);
32 void PerlIO_clearerr(PerlIO *f);
33 int PerlIO_getc(PerlIO *d);
35 int PerlIO_ungetc(PerlIO *f,int ch);
36 SSize_t PerlIO_read(PerlIO *f, void *buf, size_t numbytes);
37 int PerlIO_fileno(PerlIO *f);
39 void PerlIO_setlinebuf(PerlIO *f);
41 Off_t PerlIO_tell(PerlIO *f);
43 int PerlIO_seek(PerlIO *f, Off_t offset, int whence);
44 void PerlIO_rewind(PerlIO *f);
45 int PerlIO_getpos(PerlIO *f, SV *save); /* prototype changed */
47 int PerlIO_setpos(PerlIO *f, SV *saved); /* prototype changed */
48 int PerlIO_fast_gets(PerlIO *f);
50 int PerlIO_has_cntptr(PerlIO *f);
51 SSize_t PerlIO_get_cnt(PerlIO *f);
52 char *PerlIO_get_ptr(PerlIO *f);
53 void PerlIO_set_ptrcnt(PerlIO *f, char *ptr, SSize_t count);
54 int PerlIO_canset_cnt(PerlIO *f); /* deprecated */
56 void PerlIO_set_cnt(PerlIO *f, int count); /* deprecated */
57 int PerlIO_has_base(PerlIO *f);
59 char *PerlIO_get_base(PerlIO *f);
60 SSize_t PerlIO_get_bufsiz(PerlIO *f);
61 PerlIO *PerlIO_importFILE(FILE *stdio, const char *mode);
63 FILE *PerlIO_exportFILE(PerlIO *f, const char *mode);
64 FILE *PerlIO_findFILE(PerlIO *f);
65 void PerlIO_releaseFILE(PerlIO *f,FILE *stdio);
66 int PerlIO_apply_layers(PerlIO *f, const char *mode,
68 const char *layers);
69 int PerlIO_binmode(PerlIO *f, int ptype, int imode,
70 const char *layers);
71 void PerlIO_debug(const char *fmt,...);
72
74 Perl's source code, and extensions that want maximum portability,
75 should use the above functions instead of those defined in ANSI C's
76 stdio.h. The perl headers (in particular "perlio.h") will "#define"
77 them to the I/O mechanism selected at Configure time.
78 The functions are modeled on those in stdio.h, but parameter order has
80 been "tidied up a little".
81 "PerlIO *" takes the place of FILE *. Like FILE * it should be treated
83 as opaque (it is probably safe to assume it is a pointer to something).
84 There are currently two implementations:
86 1. USE_STDIO
88 All above are #define'd to stdio functions or are trivial wrapper
89 functions which call stdio. In this case only PerlIO * is a FILE *.
90 This has been the default implementation since the abstraction was
91 introduced in perl5.003_02.
92 2. USE_PERLIO
94 Introduced just after perl5.7.0, this is a re-implementation of the
95 above abstraction which allows perl more control over how IO is
96 done as it decouples IO from the way the operating system and C
97 library choose to do things. For USE_PERLIO PerlIO * has an extra
98 layer of indirection - it is a pointer-to-a-pointer. This allows
99 the PerlIO * to remain with a known value while swapping the
100 implementation around underneath at run time. In this case all the
101 above are true (but very simple) functions which call the
102 underlying implementation.
103 This is the only implementation for which "PerlIO_apply_layers()"
105 does anything "interesting".
106 The USE_PERLIO implementation is described in perliol.
108 Because "perlio.h" is a thin layer (for efficiency) the semantics of
110 these functions are somewhat dependent on the underlying
111 implementation. Where these variations are understood they are noted
112 below.
113 Unless otherwise noted, functions return 0 on success, or a negative
115 value (usually "EOF" which is usually -1) and set "errno" on error.
116 PerlIO_stdin(), PerlIO_stdout(), PerlIO_stderr()
118 Use these rather than "stdin", "stdout", "stderr". They are written
119 to look like "function calls" rather than variables because this
120 makes it easier to make them function calls if platform cannot
121 export data to loaded modules, or if (say) different "threads"
122 might have different values.
123 PerlIO_open(path, mode), PerlIO_fdopen(fd,mode)
125 These correspond to fopen()/fdopen() and the arguments are the
126 same. Return "NULL" and set "errno" if there is an error. There
127 may be an implementation limit on the number of open handles, which
128 may be lower than the limit on the number of open files - "errno"
129 may not be set when "NULL" is returned if this limit is exceeded.
130 PerlIO_reopen(path,mode,f)
132 While this currently exists in both implementations, perl itself
133 does not use it. As perl does not use it, it is not well tested.
134 Perl prefers to "dup" the new low-level descriptor to the
136 descriptor used by the existing PerlIO. This may become the
137 behaviour of this function in the future.
138 PerlIO_printf(f,fmt,...), PerlIO_vprintf(f,fmt,a)
140 These are fprintf()/vfprintf() equivalents.
141 PerlIO_stdoutf(fmt,...)
143 This is printf() equivalent. printf is #defined to this function,
144 so it is (currently) legal to use "printf(fmt,...)" in perl
145 sources.
146 PerlIO_read(f,buf,count), PerlIO_write(f,buf,count)
148 These correspond functionally to fread() and fwrite() but the
149 arguments and return values are different. The PerlIO_read() and
150 PerlIO_write() signatures have been modeled on the more sane low
151 level read() and write() functions instead: The "file" argument is
152 passed first, there is only one "count", and the return value can
153 distinguish between error and "EOF".
154 Returns a byte count if successful (which may be zero or positive),
156 returns negative value and sets "errno" on error. Depending on
157 implementation "errno" may be "EINTR" if operation was interrupted
158 by a signal.
159 PerlIO_close(f)
161 Depending on implementation "errno" may be "EINTR" if operation was
162 interrupted by a signal.
163 PerlIO_puts(f,s), PerlIO_putc(f,c)
165 These correspond to fputs() and fputc(). Note that arguments have
166 been revised to have "file" first.
167 PerlIO_ungetc(f,c)
169 This corresponds to ungetc(). Note that arguments have been
170 revised to have "file" first. Arranges that next read operation
171 will return the byte c. Despite the implied "character" in the
172 name only values in the range 0..0xFF are defined. Returns the byte
173 c on success or -1 ("EOF") on error. The number of bytes that can
174 be "pushed back" may vary, only 1 character is certain, and then
175 only if it is the last character that was read from the handle.
176 PerlIO_getc(f)
178 This corresponds to getc(). Despite the c in the name only byte
179 range 0..0xFF is supported. Returns the character read or -1
180 ("EOF") on error.
181 PerlIO_eof(f)
183 This corresponds to feof(). Returns a true/false indication of
184 whether the handle is at end of file. For terminal devices this
185 may or may not be "sticky" depending on the implementation. The
186 flag is cleared by PerlIO_seek(), or PerlIO_rewind().
187 PerlIO_error(f)
189 This corresponds to ferror(). Returns a true/false indication of
190 whether there has been an IO error on the handle.
191 PerlIO_fileno(f)
193 This corresponds to fileno(), note that on some platforms, the
194 meaning of "fileno" may not match Unix. Returns -1 if the handle
195 has no open descriptor associated with it.
196 PerlIO_clearerr(f)
198 This corresponds to clearerr(), i.e., clears 'error' and (usually)
199 'eof' flags for the "stream". Does not return a value.
200 PerlIO_flush(f)
202 This corresponds to fflush(). Sends any buffered write data to the
203 underlying file. If called with "NULL" this may flush all open
204 streams (or core dump with some USE_STDIO implementations).
205 Calling on a handle open for read only, or on which last operation
206 was a read of some kind may lead to undefined behaviour on some
207 USE_STDIO implementations. The USE_PERLIO (layers) implementation
208 tries to behave better: it flushes all open streams when passed
209 "NULL", and attempts to retain data on read streams either in the
210 buffer or by seeking the handle to the current logical position.
211 PerlIO_seek(f,offset,whence)
213 This corresponds to fseek(). Sends buffered write data to the
214 underlying file, or discards any buffered read data, then positions
215 the file descriptor as specified by offset and whence (sic). This
216 is the correct thing to do when switching between read and write on
217 the same handle (see issues with PerlIO_flush() above). Offset is
218 of type "Off_t" which is a perl Configure value which may not be
219 same as stdio's "off_t".
220 PerlIO_tell(f)
222 This corresponds to ftell(). Returns the current file position, or
223 (Off_t) -1 on error. May just return value system "knows" without
224 making a system call or checking the underlying file descriptor (so
225 use on shared file descriptors is not safe without a
226 PerlIO_seek()). Return value is of type "Off_t" which is a perl
227 Configure value which may not be same as stdio's "off_t".
228 PerlIO_getpos(f,p), PerlIO_setpos(f,p)
230 These correspond (loosely) to fgetpos() and fsetpos(). Rather than
231 stdio's Fpos_t they expect a "Perl Scalar Value" to be passed. What
232 is stored there should be considered opaque. The layout of the data
233 may vary from handle to handle. When not using stdio or if
234 platform does not have the stdio calls then they are implemented in
235 terms of PerlIO_tell() and PerlIO_seek().
236 PerlIO_rewind(f)
238 This corresponds to rewind(). It is usually defined as being
239 PerlIO_seek(f,(Off_t)0L, SEEK_SET);
241 PerlIO_clearerr(f);
242 PerlIO_tmpfile()
244 This corresponds to tmpfile(), i.e., returns an anonymous PerlIO or
245 NULL on error. The system will attempt to automatically delete the
246 file when closed. On Unix the file is usually "unlink"-ed just
247 after it is created so it does not matter how it gets closed. On
248 other systems the file may only be deleted if closed via
249 PerlIO_close() and/or the program exits via "exit". Depending on
250 the implementation there may be "race conditions" which allow other
251 processes access to the file, though in general it will be safer in
252 this regard than ad. hoc. schemes.
253 PerlIO_setlinebuf(f)
255 This corresponds to setlinebuf(). Does not return a value. What
256 constitutes a "line" is implementation dependent but usually means
257 that writing "\n" flushes the buffer. What happens with things
258 like "this\nthat" is uncertain. (Perl core uses it only when
259 "dumping"; it has nothing to do with $| auto-flush.)
260 Co-existence with stdio
262 There is outline support for co-existence of PerlIO with stdio.
263 Obviously if PerlIO is implemented in terms of stdio there is no
264 problem. However in other cases then mechanisms must exist to create a
265 FILE * which can be passed to library code which is going to use stdio
266 calls.
267 The first step is to add this line:
269 #define PERLIO_NOT_STDIO 0
271 before including any perl header files. (This will probably become the
273 default at some point). That prevents "perlio.h" from attempting to
274 #define stdio functions onto PerlIO functions.
275 XS code is probably better using "typemap" if it expects FILE *
277 arguments. The standard typemap will be adjusted to comprehend any
278 changes in this area.
279 PerlIO_importFILE(f,mode)
281 Used to get a PerlIO * from a FILE *.
282 The mode argument should be a string as would be passed to
284 fopen/PerlIO_open. If it is NULL then - for legacy support - the
285 code will (depending upon the platform and the implementation)
286 either attempt to empirically determine the mode in which f is
287 open, or use "r+" to indicate a read/write stream.
288 Once called the FILE * should ONLY be closed by calling
290 "PerlIO_close()" on the returned PerlIO *.
291 The PerlIO is set to textmode. Use PerlIO_binmode if this is not
293 the desired mode.
294 This is not the reverse of PerlIO_exportFILE().
296 PerlIO_exportFILE(f,mode)
298 Given a PerlIO * create a 'native' FILE * suitable for passing to
299 code expecting to be compiled and linked with ANSI C stdio.h. The
300 mode argument should be a string as would be passed to
301 fopen/PerlIO_open. If it is NULL then - for legacy support - the
302 FILE * is opened in same mode as the PerlIO *.
303 The fact that such a FILE * has been 'exported' is recorded,
305 (normally by pushing a new :stdio "layer" onto the PerlIO *), which
306 may affect future PerlIO operations on the original PerlIO *. You
307 should not call "fclose()" on the file unless you call
308 "PerlIO_releaseFILE()" to disassociate it from the PerlIO *. (Do
309 not use PerlIO_importFILE() for doing the disassociation.)
310 Calling this function repeatedly will create a FILE * on each call
312 (and will push an :stdio layer each time as well).
313 PerlIO_releaseFILE(p,f)
315 Calling PerlIO_releaseFILE informs PerlIO that all use of FILE * is
316 complete. It is removed from the list of 'exported' FILE *s, and
317 the associated PerlIO * should revert to its original behaviour.
318 Use this to disassociate a file from a PerlIO * that was associated
320 using PerlIO_exportFILE().
321 PerlIO_findFILE(f)
323 Returns a native FILE * used by a stdio layer. If there is none, it
324 will create one with PerlIO_exportFILE. In either case the FILE *
325 should be considered as belonging to PerlIO subsystem and should
326 only be closed by calling "PerlIO_close()".
327 "Fast gets" Functions
329 In addition to standard-like API defined so far above there is an
330 "implementation" interface which allows perl to get at internals of
331 PerlIO. The following calls correspond to the various FILE_xxx macros
332 determined by Configure - or their equivalent in other implementations.
333 This section is really of interest to only those concerned with
334 detailed perl-core behaviour, implementing a PerlIO mapping or writing
335 code which can make use of the "read ahead" that has been done by the
336 IO system in the same way perl does. Note that any code that uses these
337 interfaces must be prepared to do things the traditional way if a
338 handle does not support them.
339 PerlIO_fast_gets(f)
341 Returns true if implementation has all the interfaces required to
342 allow perl's "sv_gets" to "bypass" normal IO mechanism. This can
343 vary from handle to handle.
344 PerlIO_fast_gets(f) = PerlIO_has_cntptr(f) && \
346 PerlIO_canset_cnt(f) && \
347 'Can set pointer into buffer'
348 PerlIO_has_cntptr(f)
350 Implementation can return pointer to current position in the
351 "buffer" and a count of bytes available in the buffer. Do not use
352 this - use PerlIO_fast_gets.
353 PerlIO_get_cnt(f)
355 Return count of readable bytes in the buffer. Zero or negative
356 return means no more bytes available.
357 PerlIO_get_ptr(f)
359 Return pointer to next readable byte in buffer, accessing via the
360 pointer (dereferencing) is only safe if PerlIO_get_cnt() has
361 returned a positive value. Only positive offsets up to value
362 returned by PerlIO_get_cnt() are allowed.
363 PerlIO_set_ptrcnt(f,p,c)
365 Set pointer into buffer, and a count of bytes still in the buffer.
366 Should be used only to set pointer to within range implied by
367 previous calls to "PerlIO_get_ptr" and "PerlIO_get_cnt". The two
368 values must be consistent with each other (implementation may only
369 use one or the other or may require both).
370 PerlIO_canset_cnt(f)
372 Implementation can adjust its idea of number of bytes in the
373 buffer. Do not use this - use PerlIO_fast_gets.
374 PerlIO_set_cnt(f,c)
376 Obscure - set count of bytes in the buffer. Deprecated. Only
377 usable if PerlIO_canset_cnt() returns true. Currently used in only
378 doio.c to force count less than -1 to -1. Perhaps should be
379 PerlIO_set_empty or similar. This call may actually do nothing if
380 "count" is deduced from pointer and a "limit". Do not use this -
381 use PerlIO_set_ptrcnt().
382 PerlIO_has_base(f)
384 Returns true if implementation has a buffer, and can return pointer
385 to whole buffer and its size. Used by perl for -T / -B tests.
386 Other uses would be very obscure...
387 PerlIO_get_base(f)
389 Return start of buffer. Access only positive offsets in the buffer
390 up to the value returned by PerlIO_get_bufsiz().
391 PerlIO_get_bufsiz(f)
393 Return the total number of bytes in the buffer, this is neither the
394 number that can be read, nor the amount of memory allocated to the
395 buffer. Rather it is what the operating system and/or
396 implementation happened to "read()" (or whatever) last time IO was
397 requested.
398 Other Functions
400 PerlIO_apply_layers(f,mode,layers)
401 The new interface to the USE_PERLIO implementation. The layers
402 ":crlf" and ":raw" are only ones allowed for other implementations
403 and those are silently ignored. (As of perl5.8 ":raw" is
404 deprecated.) Use PerlIO_binmode() below for the portable case.
405 PerlIO_binmode(f,ptype,imode,layers)
407 The hook used by perl's "binmode" operator. ptype is perl's
408 character for the kind of IO:
409 '<' read
411 '>' write
412 '+' read/write
413 imode is "O_BINARY" or "O_TEXT".
415 layers is a string of layers to apply, only ":crlf" makes sense in
417 the non USE_PERLIO case. (As of perl5.8 ":raw" is deprecated in
418 favour of passing NULL.)
419 Portable cases are:
421 PerlIO_binmode(f,ptype,O_BINARY,NULL);
423 and
424 PerlIO_binmode(f,ptype,O_TEXT,":crlf");
425 On Unix these calls probably have no effect whatsoever. Elsewhere
427 they alter "\n" to CR,LF translation and possibly cause a special
428 text "end of file" indicator to be written or honoured on read. The
429 effect of making the call after doing any IO to the handle depends
430 on the implementation. (It may be ignored, affect any data which is
431 already buffered as well, or only apply to subsequent data.)
432 PerlIO_debug(fmt,...)
434 PerlIO_debug is a printf()-like function which can be used for
435 debugging. No return value. Its main use is inside PerlIO where
436 using real printf, warn() etc. would recursively call PerlIO and be
437 a problem.
438 PerlIO_debug writes to the file named by $ENV{'PERLIO_DEBUG'} or
440 defaults to stderr if the environment variable is not defined.
441 Typical use might be
442 Bourne shells (sh, ksh, bash, zsh, ash, ...):
444 PERLIO_DEBUG=/tmp/perliodebug.log ./perl -Di somescript some args
445 Csh/Tcsh:
447 setenv PERLIO_DEBUG /tmp/perliodebug.log
448 ./perl -Di somescript some args
449 If you have the "env" utility:
451 env PERLIO_DEBUG=/tmp/perliodebug.log ./perl -Di somescript args
452 Win32:
454 set PERLIO_DEBUG=perliodebug.log
455 perl -Di somescript some args
456 On a Perl built without "-DDEBUGGING", or when the "-Di" command-
458 line switch is not specified, or under taint, PerlIO_debug() is a
459 no-op.
460perl v5.34.0 2021-10-18 PERLAPIO(1)