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, int flags);
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 three 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 all three implementations perl
133 itself does not use it. As perl does not use it, it is not well
134 tested.
135 Perl prefers to "dup" the new low-level descriptor to the
137 descriptor used by the existing PerlIO. This may become the
138 behaviour of this function in the future.
139 PerlIO_printf(f,fmt,...), PerlIO_vprintf(f,fmt,a)
141 These are fprintf()/vfprintf() equivalents.
142 PerlIO_stdoutf(fmt,...)
144 This is printf() equivalent. printf is #defined to this function,
145 so it is (currently) legal to use "printf(fmt,...)" in perl
146 sources.
147 PerlIO_read(f,buf,count), PerlIO_write(f,buf,count)
149 These correspond functionally to fread() and fwrite() but the
150 arguments and return values are different. The PerlIO_read() and
151 PerlIO_write() signatures have been modeled on the more sane low
152 level read() and write() functions instead: The "file" argument is
153 passed first, there is only one "count", and the return value can
154 distinguish between error and "EOF".
155 Returns a byte count if successful (which may be zero or positive),
157 returns negative value and sets "errno" on error. Depending on
158 implementation "errno" may be "EINTR" if operation was interrupted
159 by a signal.
160 PerlIO_close(f)
162 Depending on implementation "errno" may be "EINTR" if operation was
163 interrupted by a signal.
164 PerlIO_puts(f,s), PerlIO_putc(f,c)
166 These correspond to fputs() and fputc(). Note that arguments have
167 been revised to have "file" first.
168 PerlIO_ungetc(f,c)
170 This corresponds to ungetc(). Note that arguments have been
171 revised to have "file" first. Arranges that next read operation
172 will return the byte c. Despite the implied "character" in the
173 name only values in the range 0..0xFF are defined. Returns the byte
174 c on success or -1 ("EOF") on error. The number of bytes that can
175 be "pushed back" may vary, only 1 character is certain, and then
176 only if it is the last character that was read from the handle.
177 PerlIO_getc(f)
179 This corresponds to getc(). Despite the c in the name only byte
180 range 0..0xFF is supported. Returns the character read or -1
181 ("EOF") on error.
182 PerlIO_eof(f)
184 This corresponds to feof(). Returns a true/false indication of
185 whether the handle is at end of file. For terminal devices this
186 may or may not be "sticky" depending on the implementation. The
187 flag is cleared by PerlIO_seek(), or PerlIO_rewind().
188 PerlIO_error(f)
190 This corresponds to ferror(). Returns a true/false indication of
191 whether there has been an IO error on the handle.
192 PerlIO_fileno(f)
194 This corresponds to fileno(), note that on some platforms, the
195 meaning of "fileno" may not match Unix. Returns -1 if the handle
196 has no open descriptor associated with it.
197 PerlIO_clearerr(f)
199 This corresponds to clearerr(), i.e., clears 'error' and (usually)
200 'eof' flags for the "stream". Does not return a value.
201 PerlIO_flush(f)
203 This corresponds to fflush(). Sends any buffered write data to the
204 underlying file. If called with "NULL" this may flush all open
205 streams (or core dump with some USE_STDIO implementations).
206 Calling on a handle open for read only, or on which last operation
207 was a read of some kind may lead to undefined behaviour on some
208 USE_STDIO implementations. The USE_PERLIO (layers) implementation
209 tries to behave better: it flushes all open streams when passed
210 "NULL", and attempts to retain data on read streams either in the
211 buffer or by seeking the handle to the current logical position.
212 PerlIO_seek(f,offset,whence)
214 This corresponds to fseek(). Sends buffered write data to the
215 underlying file, or discards any buffered read data, then positions
216 the file descriptor as specified by offset and whence (sic). This
217 is the correct thing to do when switching between read and write on
218 the same handle (see issues with PerlIO_flush() above). Offset is
219 of type "Off_t" which is a perl Configure value which may not be
220 same as stdio's "off_t".
221 PerlIO_tell(f)
223 This corresponds to ftell(). Returns the current file position, or
224 (Off_t) -1 on error. May just return value system "knows" without
225 making a system call or checking the underlying file descriptor (so
226 use on shared file descriptors is not safe without a
227 PerlIO_seek()). Return value is of type "Off_t" which is a perl
228 Configure value which may not be same as stdio's "off_t".
229 PerlIO_getpos(f,p), PerlIO_setpos(f,p)
231 These correspond (loosely) to fgetpos() and fsetpos(). Rather than
232 stdio's Fpos_t they expect a "Perl Scalar Value" to be passed. What
233 is stored there should be considered opaque. The layout of the data
234 may vary from handle to handle. When not using stdio or if
235 platform does not have the stdio calls then they are implemented in
236 terms of PerlIO_tell() and PerlIO_seek().
237 PerlIO_rewind(f)
239 This corresponds to rewind(). It is usually defined as being
240 PerlIO_seek(f,(Off_t)0L, SEEK_SET);
242 PerlIO_clearerr(f);
243 PerlIO_tmpfile()
245 This corresponds to tmpfile(), i.e., returns an anonymous PerlIO or
246 NULL on error. The system will attempt to automatically delete the
247 file when closed. On Unix the file is usually "unlink"-ed just
248 after it is created so it does not matter how it gets closed. On
249 other systems the file may only be deleted if closed via
250 PerlIO_close() and/or the program exits via "exit". Depending on
251 the implementation there may be "race conditions" which allow other
252 processes access to the file, though in general it will be safer in
253 this regard than ad. hoc. schemes.
254 PerlIO_setlinebuf(f)
256 This corresponds to setlinebuf(). Does not return a value. What
257 constitutes a "line" is implementation dependent but usually means
258 that writing "\n" flushes the buffer. What happens with things
259 like "this\nthat" is uncertain. (Perl core uses it only when
260 "dumping"; it has nothing to do with $| auto-flush.)
261 Co-existence with stdio
263 There is outline support for co-existence of PerlIO with stdio.
264 Obviously if PerlIO is implemented in terms of stdio there is no
265 problem. However in other cases then mechanisms must exist to create a
266 FILE * which can be passed to library code which is going to use stdio
267 calls.
268 The first step is to add this line:
270 #define PERLIO_NOT_STDIO 0
272 before including any perl header files. (This will probably become the
274 default at some point). That prevents "perlio.h" from attempting to
275 #define stdio functions onto PerlIO functions.
276 XS code is probably better using "typemap" if it expects FILE *
278 arguments. The standard typemap will be adjusted to comprehend any
279 changes in this area.
280 PerlIO_importFILE(f,mode)
282 Used to get a PerlIO * from a FILE *.
283 The mode argument should be a string as would be passed to
285 fopen/PerlIO_open. If it is NULL then - for legacy support - the
286 code will (depending upon the platform and the implementation)
287 either attempt to empirically determine the mode in which f is
288 open, or use "r+" to indicate a read/write stream.
289 Once called the FILE * should ONLY be closed by calling
291 "PerlIO_close()" on the returned PerlIO *.
292 The PerlIO is set to textmode. Use PerlIO_binmode if this is not
294 the desired mode.
295 This is not the reverse of PerlIO_exportFILE().
297 PerlIO_exportFILE(f,mode)
299 Given a PerlIO * create a 'native' FILE * suitable for passing to
300 code expecting to be compiled and linked with ANSI C stdio.h. The
301 mode argument should be a string as would be passed to
302 fopen/PerlIO_open. If it is NULL then - for legacy support - the
303 FILE * is opened in same mode as the PerlIO *.
304 The fact that such a FILE * has been 'exported' is recorded,
306 (normally by pushing a new :stdio "layer" onto the PerlIO *), which
307 may affect future PerlIO operations on the original PerlIO *. You
308 should not call "fclose()" on the file unless you call
309 "PerlIO_releaseFILE()" to disassociate it from the PerlIO *. (Do
310 not use PerlIO_importFILE() for doing the disassociation.)
311 Calling this function repeatedly will create a FILE * on each call
313 (and will push an :stdio layer each time as well).
314 PerlIO_releaseFILE(p,f)
316 Calling PerlIO_releaseFILE informs PerlIO that all use of FILE * is
317 complete. It is removed from the list of 'exported' FILE *s, and
318 the associated PerlIO * should revert to its original behaviour.
319 Use this to disassociate a file from a PerlIO * that was associated
321 using PerlIO_exportFILE().
322 PerlIO_findFILE(f)
324 Returns a native FILE * used by a stdio layer. If there is none, it
325 will create one with PerlIO_exportFILE. In either case the FILE *
326 should be considered as belonging to PerlIO subsystem and should
327 only be closed by calling "PerlIO_close()".
328 "Fast gets" Functions
330 In addition to standard-like API defined so far above there is an
331 "implementation" interface which allows perl to get at internals of
332 PerlIO. The following calls correspond to the various FILE_xxx macros
333 determined by Configure - or their equivalent in other implementations.
334 This section is really of interest to only those concerned with
335 detailed perl-core behaviour, implementing a PerlIO mapping or writing
336 code which can make use of the "read ahead" that has been done by the
337 IO system in the same way perl does. Note that any code that uses these
338 interfaces must be prepared to do things the traditional way if a
339 handle does not support them.
340 PerlIO_fast_gets(f)
342 Returns true if implementation has all the interfaces required to
343 allow perl's "sv_gets" to "bypass" normal IO mechanism. This can
344 vary from handle to handle.
345 PerlIO_fast_gets(f) = PerlIO_has_cntptr(f) && \
347 PerlIO_canset_cnt(f) && \
348 'Can set pointer into buffer'
349 PerlIO_has_cntptr(f)
351 Implementation can return pointer to current position in the
352 "buffer" and a count of bytes available in the buffer. Do not use
353 this - use PerlIO_fast_gets.
354 PerlIO_get_cnt(f)
356 Return count of readable bytes in the buffer. Zero or negative
357 return means no more bytes available.
358 PerlIO_get_ptr(f)
360 Return pointer to next readable byte in buffer, accessing via the
361 pointer (dereferencing) is only safe if PerlIO_get_cnt() has
362 returned a positive value. Only positive offsets up to value
363 returned by PerlIO_get_cnt() are allowed.
364 PerlIO_set_ptrcnt(f,p,c)
366 Set pointer into buffer, and a count of bytes still in the buffer.
367 Should be used only to set pointer to within range implied by
368 previous calls to "PerlIO_get_ptr" and "PerlIO_get_cnt". The two
369 values must be consistent with each other (implementation may only
370 use one or the other or may require both).
371 PerlIO_canset_cnt(f)
373 Implementation can adjust its idea of number of bytes in the
374 buffer. Do not use this - use PerlIO_fast_gets.
375 PerlIO_set_cnt(f,c)
377 Obscure - set count of bytes in the buffer. Deprecated. Only
378 usable if PerlIO_canset_cnt() returns true. Currently used in only
379 doio.c to force count less than -1 to -1. Perhaps should be
380 PerlIO_set_empty or similar. This call may actually do nothing if
381 "count" is deduced from pointer and a "limit". Do not use this -
382 use PerlIO_set_ptrcnt().
383 PerlIO_has_base(f)
385 Returns true if implementation has a buffer, and can return pointer
386 to whole buffer and its size. Used by perl for -T / -B tests.
387 Other uses would be very obscure...
388 PerlIO_get_base(f)
390 Return start of buffer. Access only positive offsets in the buffer
391 up to the value returned by PerlIO_get_bufsiz().
392 PerlIO_get_bufsiz(f)
394 Return the total number of bytes in the buffer, this is neither the
395 number that can be read, nor the amount of memory allocated to the
396 buffer. Rather it is what the operating system and/or
397 implementation happened to "read()" (or whatever) last time IO was
398 requested.
399 Other Functions
401 PerlIO_apply_layers(f,mode,layers)
402 The new interface to the USE_PERLIO implementation. The layers
403 ":crlf" and ":raw" are only ones allowed for other implementations
404 and those are silently ignored. (As of perl5.8 ":raw" is
405 deprecated.) Use PerlIO_binmode() below for the portable case.
406 PerlIO_binmode(f,ptype,imode,layers)
408 The hook used by perl's "binmode" operator. ptype is perl's
409 character for the kind of IO:
410 '<' read
412 '>' write
413 '+' read/write
414 imode is "O_BINARY" or "O_TEXT".
416 layers is a string of layers to apply, only ":crlf" makes sense in
418 the non USE_PERLIO case. (As of perl5.8 ":raw" is deprecated in
419 favour of passing NULL.)
420 Portable cases are:
422 PerlIO_binmode(f,ptype,O_BINARY,NULL);
424 and
425 PerlIO_binmode(f,ptype,O_TEXT,":crlf");
426 On Unix these calls probably have no effect whatsoever. Elsewhere
428 they alter "\n" to CR,LF translation and possibly cause a special
429 text "end of file" indicator to be written or honoured on read. The
430 effect of making the call after doing any IO to the handle depends
431 on the implementation. (It may be ignored, affect any data which is
432 already buffered as well, or only apply to subsequent data.)
433 PerlIO_debug(fmt,...)
435 PerlIO_debug is a printf()-like function which can be used for
436 debugging. No return value. Its main use is inside PerlIO where
437 using real printf, warn() etc. would recursively call PerlIO and be
438 a problem.
439 PerlIO_debug writes to the file named by $ENV{'PERLIO_DEBUG'} or
441 defaults to stderr if the environment variable is not defined.
442 Typical use might be
443 Bourne shells (sh, ksh, bash, zsh, ash, ...):
445 PERLIO_DEBUG=/tmp/perliodebug.log ./perl -Di somescript some args
446 Csh/Tcsh:
448 setenv PERLIO_DEBUG /tmp/perliodebug.log
449 ./perl -Di somescript some args
450 If you have the "env" utility:
452 env PERLIO_DEBUG=/tmp/perliodebug.log ./perl -Di somescript args
453 Win32:
455 set PERLIO_DEBUG=perliodebug.log
456 perl -Di somescript some args
457 On a Perl built without "-DDEBUGGING", or when the "-Di" command-
459 line switch is not specified, or under taint, PerlIO_debug() is a
460 no-op.
461perl v5.26.3 2018-03-01 PERLAPIO(1)