3 perlapio - perl's IO abstraction interface.
7 #define PERLIO_NOT_STDIO 0 /* For co-existence with stdio only */
8 #include <perlio.h> /* Usually via #include <perl.h> */
10 PerlIO *PerlIO_stdin(void);
11 PerlIO *PerlIO_stdout(void);
12 PerlIO *PerlIO_stderr(void);
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);
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);
27 int PerlIO_eof(PerlIO *f);
28 int PerlIO_error(PerlIO *f);
29 void PerlIO_clearerr(PerlIO *f);
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);
35 int PerlIO_fileno(PerlIO *f);
37 void PerlIO_setlinebuf(PerlIO *f);
39 Off_t PerlIO_tell(PerlIO *f);
40 int PerlIO_seek(PerlIO *f, Off_t offset, int whence);
41 void PerlIO_rewind(PerlIO *f);
43 int PerlIO_getpos(PerlIO *f, SV *save); /* prototype changed */
44 int PerlIO_setpos(PerlIO *f, SV *saved); /* prototype changed */
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);
52 int PerlIO_canset_cnt(PerlIO *f); /* deprecated */
53 void PerlIO_set_cnt(PerlIO *f, int count); /* deprecated */
55 int PerlIO_has_base(PerlIO *f);
56 char *PerlIO_get_base(PerlIO *f);
57 int PerlIO_get_bufsiz(PerlIO *f);
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);
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,...)
70 Perl's source code, and extensions that want maximum portability, should use the above
71 functions instead of those defined in ANSI C's I<stdio.h>. The perl headers (in
72 particular "perlio.h") will C<#define> them to the I/O mechanism selected at Configure time.
74 The functions are modeled on those in I<stdio.h>, but parameter order
75 has been "tidied up a little".
77 C<PerlIO *> takes the place of FILE *. Like FILE * it should be treated as
78 opaque (it is probably safe to assume it is a pointer to something).
80 There are currently three implementations:
86 All above are #define'd to stdio functions or are trivial wrapper functions which
87 call stdio. In this case I<only> PerlIO * is a FILE *.
88 This has been the default implementation since the abstraction was introduced
93 A "legacy" implementation in terms of the "sfio" library. Used for some specialist
94 applications on Unix machines ("sfio" is not widely ported away from Unix).
95 Most of above are #define'd to the sfio functions. PerlIO * is in this case Sfio_t *.
99 Introduced just after perl5.7.0 this is a re-implementation of the above abstraction
100 which allows perl more control over how IO is done as it decouples IO from the
101 way the operating system and C library choose to do things. For USE_PERLIO
102 PerlIO * has an extra layer of indirection - it is a pointer-to-a-pointer.
103 This allows the PerlIO * to remain with a known value while swapping the
104 implementation arround underneath I<at run time>. In this case all the
105 above are true (but very simple) functions which call the underlying implementation.
107 This is the only implementation for which C<PerlIO_apply_layers()> does anything
110 The USE_PERLIO implementation is described in L<perliol>.
114 Because "perlio.h" is a thing layer (for efficiency) the semantics of these functions are
115 somewhat dependent on the the underlying implementation. Where these variations are
116 understood they are noted below.
118 Unless otherwise noted, functions return 0 on success, or a negative value (usually
119 C<EOF> which is usually -1) and set C<errno> on error.
123 =item B<PerlIO_stdin()>, B<PerlIO_stdout()>, B<PerlIO_stderr()>
125 Use these rather than C<stdin>, C<stdout>, C<stderr>. They are written
126 to look like "function calls" rather than variables because this makes
127 it easier to I<make them> function calls if platform cannot export data
128 to loaded modules, or if (say) different "threads" might have different
131 =item B<PerlIO_open(path, mode)>, B<PerlIO_fdopen(fd,mode)>
133 These correspond to fopen()/fdopen() and the arguments are the same.
134 Return C<NULL> and set C<errno> if there is an error.
135 There may be an implementation limit on the number of open handles, which may
136 be lower than the limit on the number of open files - C<errno> may
137 not be set when C<NULL> is returned if this limnit is exceeded.
139 =item B<PerlIO_reopen(path,mode,f)
141 While this currently exists in all three implementations perl itself
142 does not use it. I<As perl does not use it, it is not well tested.>
144 Perl prefers to C<dup> the new low-level descriptor to the descriptor used
145 by the existing PerlIO. This may become the behaviour of this function
148 =item B<PerlIO_printf(f,fmt,...)>, B<PerlIO_vprintf(f,fmt,a)>
150 These are fprintf()/vfprintf() equivalents.
152 =item B<PerlIO_stdoutf(fmt,...)>
154 This is printf() equivalent. printf is #defined to this function,
155 so it is (currently) legal to use C<printf(fmt,...)> in perl sources.
157 =item B<PerlIO_read(f,buf,count)>, B<PerlIO_write(f,buf,count)>
159 These correspond to fread() and fwrite(). Note that arguments
160 are different, there is only one "count" and order has
161 "file" first. Returns a byte count if successful (which may be zero),
162 returns negative value and sets C<errno> on error.
163 Depending on implementation C<errno> may be C<EINTR> if operation
164 was interrupted by a signal.
166 =item B<PerlIO_close(f)>
168 Depending on implementation C<errno> may be C<EINTR> if operation
169 was interrupted by a signal.
171 =item B<PerlIO_puts(f,s)>, B<PerlIO_putc(f,c)>
173 These correspond to fputs() and fputc().
174 Note that arguments have been revised to have "file" first.
176 =item B<PerlIO_ungetc(f,c)>
178 This corresponds to ungetc().
179 Note that arguments have been revised to have "file" first.
180 Arranges that next read operation will return the byte B<c>.
181 Despite the implied "character" in the name only values in the
182 range 0..0xFF are defined. Returns the byte B<c> on success or -1 (C<EOF>) on error.
183 The number of bytes that can be "pushed back" may vary, only 1 character is
184 certain, and then only if it is the last character that was read from the handle.
186 =item B<PerlIO_getc(f)>
188 This corresponds to getc().
189 Despite the c in the name only byte range 0..0xFF is supported.
190 Returns the character read or -1 (C<EOF>) on error.
192 =item B<PerlIO_eof(f)>
194 This corresponds to feof().
195 Returns a true/false indication of whether the handle is at end of file.
196 For terminal devices this may or may not be "sticky" depending on the implementation.
197 The flag is cleared by PerlIO_seek(), or PerlIO_rewind().
199 =item B<PerlIO_error(f)>
201 This corresponds to ferror().
202 Returns a true/false indication of whether there has been an IO error on the handle.
204 =item B<PerlIO_fileno(f)>
206 This corresponds to fileno(), note that on some platforms,
207 the meaning of "fileno" may not match Unix. Returns -1 if the handle has no
208 open descriptor associated with it.
210 =item B<PerlIO_clearerr(f)>
212 This corresponds to clearerr(), i.e., clears 'error' and (usually) 'eof'
213 flags for the "stream". Does not return a value.
215 =item B<PerlIO_flush(f)>
217 This corresponds to fflush().
218 Sends any buffered write data to the underlying file.
219 If called with C<NULL> this may flush all open streams (or core dump).
220 Calling on a handle open for read only, or on which last operation was a read of some kind
221 may lead to undefined behaviour.
223 =item B<PerlIO_seek(f,offset,whence)>
225 This corresponds to fseek().
226 Sends buffered write data to the underlying file, or discards any buffered
227 read data, then positions the file desciptor as specified by B<offset> and B<whence> (sic).
228 This is the correct thing to do when switching between read and write on the same
229 handle (see issues with PerlIO_flush() above).
230 Offset is of type C<Off_t> which is a perl Configure value which may not be same
233 =item B<PerlIO_tell(f)>
235 This corresponds to ftell().
236 Returns the current file position, or (Off_t) -1 on error.
237 May just return value system "knows" without making a system call or checking
238 the underlying file descriptor (so use on shared file descriptors is not
239 safe without a PerlIO_seek()). Return value is of type C<Off_t> which is a perl Configure
240 value which may not be same as stdio's C<off_t>.
242 =item B<PerlIO_getpos(f,p)>, B<PerlIO_setpos(f,p)>
244 These correspond (loosely) to fgetpos() and fsetpos(). Rather than stdio's Fpos_t
245 they expect a "Perl Scalar Value" to be passed. What is stored there should
246 be considered opaque. The layout of the data may vary from handle to handle.
247 When not using stdio or if platform does not have the stdio calls then they are
248 implemented in terms of PerlIO_tell() and PerlIO_seek().
250 =item B<PerlIO_rewind(f)>
252 This corresponds to rewind(). It is usually defined as being
254 PerlIO_seek(f,(Off_t)0L, SEEK_SET);
258 =item B<PerlIO_tmpfile()>
260 This corresponds to tmpfile(), i.e., returns an anonymous
261 PerlIO or NULL on error.
262 The system will attempt to automatically delete the file when closed.
263 On Unix the file is usually C<unlink>-ed just after
264 it is created so it does not matter how it gets closed. On other systems the file may
265 only be deleted if closed via PerlIO_close() and/or the program exits via C<exit>.
266 Depending on the implementation there may be "race conditions" which allow other
267 processes access to the file, though in general it will be safer in this regard
268 than ad. hoc. schemes.
270 =item B<PerlIO_setlinebuf(f)>
272 This corresponds to setlinebuf().
273 Does not return a value. What constitutes a "line" is implementation
274 dependent but usually means that writing "\n" flushes the buffer.
275 What happens with things like "this\nthat" is uncertain.
276 (Perl core uses it I<only> when "dumping"; it has nothing to do with $| auto-flush.)
280 =head2 Co-existence with stdio
282 There is outline support for co-existence of PerlIO with stdio.
283 Obviously if PerlIO is implemented in terms of stdio there is
284 no problem. However in other cases then mechanisms must exist to create a FILE *
285 which can be passed to library code which is going to use stdio calls.
287 The fisrt step is to add this line:
289 #define PERLIO_NOT_STDIO 0
291 I<before> including any perl header files. (This will probably become the
292 default at some point). That prevents "perlio.h" from attempting to
293 #define stdio functions onto PerlIO functions.
295 XS code is probably better using "typemap" if it expects FILE * arguments.
296 The standard typemap will be adjusted to comprehend any changes in this area.
300 =item B<PerlIO_importFILE(f,flags)>
302 Used to get a PerlIO * from a FILE *.
303 May need additional arguments, interface under review.
305 The flags argument was meant to be used for read vs write vs read/write
306 information. In hindsight it would have been better to make it a char *mode
309 =item B<PerlIO_exportFILE(f,flags)>
311 Given a PerlIO * return a 'native' FILE * suitable for
312 passing to code expecting to be compiled and linked with
315 The fact that such a FILE * has been 'exported' is recorded,
316 and may affect future PerlIO operations on the original
319 =item B<PerlIO_findFILE(f)>
321 Returns previously 'exported' FILE * (if any).
322 Place holder until interface is fully defined.
324 =item B<PerlIO_releaseFILE(p,f)>
326 Calling PerlIO_releaseFILE informs PerlIO that all use
327 of FILE * is complete. It is removed from list of 'exported'
328 FILE *s, and associated PerlIO * should revert to original
333 =head2 "Fast gets" Functions
335 In addition to standard-like API defined so far above there is an "implementation" interface
336 which allows perl to get at internals of PerlIO.
337 The following calls correspond to the various FILE_xxx macros determined
338 by Configure - or their equivalent in other implementations. This section is really of
339 interest to only those concerned with detailed perl-core behaviour, implementing a
340 PerlIO mapping or writing code which can make use of the "read ahead" that has been done by
341 the IO system in the same way perl does. Note that any code that uses these interfaces
342 must be prepared to do things the traditional way if a handle does not support
347 =item B<PerlIO_fast_gets(f)>
349 Returns true if implementation has all the interfaces required to
350 allow perl's C<sv_gets> to "bypass" normal IO mechanism.
351 This can vary from handle to handle.
353 PerlIO_fast_gets(f) = PerlIO_has_cntptr(f) && \
354 PerlIO_canset_cnt(f) && \
355 `Can set pointer into buffer'
358 =item B<PerlIO_has_cntptr(f)>
360 Implementation can return pointer to current position in the "buffer" and
361 a count of bytes available in the buffer.
362 Do not use this - use PerlIO_fast_gets.
364 =item B<PerlIO_get_cnt(f)>
366 Return count of readable bytes in the buffer. Zero or negative return means
367 no more bytes available.
369 =item B<PerlIO_get_ptr(f)>
371 Return pointer to next readable byte in buffer, accessing via the pointer
372 (dereferencing) is only safe if PerlIO_get_cnt() has returned a positive value.
373 Only positive offsets up to value returned by PerlIO_get_cnt() are allowed.
375 =item B<PerlIO_set_ptrcnt(f,p,c)>
377 Set pointer into buffer, and a count of bytes still in the
378 buffer. Should be used only to set
379 pointer to within range implied by previous calls
380 to C<PerlIO_get_ptr> and C<PerlIO_get_cnt>. The two values I<must> be consistent
381 with each other (implementation may only use one or the other or may require both).
383 =item B<PerlIO_canset_cnt(f)>
385 Implementation can adjust its idea of number of bytes in the buffer.
386 Do not use this - use PerlIO_fast_gets.
388 =item B<PerlIO_set_cnt(f,c)>
390 Obscure - set count of bytes in the buffer. Deprecated.
391 Only usable if PerlIO_canset_cnt() returns true.
392 Currently used in only doio.c to force count < -1 to -1.
393 Perhaps should be PerlIO_set_empty or similar.
394 This call may actually do nothing if "count" is deduced from pointer
396 Do not use this - use PerlIO_set_ptrcnt().
398 =item B<PerlIO_has_base(f)>
400 Returns true if implementation has a buffer, and can return pointer
401 to whole buffer and its size. Used by perl for B<-T> / B<-B> tests.
402 Other uses would be very obscure...
404 =item B<PerlIO_get_base(f)>
406 Return I<start> of buffer. Access only positive offsets in the buffer
407 up to the value returned by PerlIO_get_bufsiz().
409 =item B<PerlIO_get_bufsiz(f)>
411 Return the I<total number of bytes> in the buffer, this is neither the number
412 that can be read, nor the amount of memory allocated to the buffer. Rather
413 it is what the operating system and/or implementation happened to C<read()>
414 (or whatever) last time IO was requested.
418 =head2 Other Functions
422 =item PerlIO_apply_layers(f,mode,layers)
424 The new interface to the USE_PERLIO implementation. The layers ":crlf"
425 and ":raw" are only ones allowed for other implementations and those
426 are silently ignored. Use PerlIO_binmode() below for the portable
429 =item PerlIO_binmode(f,ptype,imode,layers)
431 The hook used by perl's C<binmode> operator.
432 B<ptype> is perl's charcter for the kind of IO:
444 B<imode> is C<O_BINARY> or C<O_TEXT>.
446 B<layers> is a string of layers to apply, only ":raw" or :"crlf" make
447 sense in the non USE_PERLIO case.
451 PerlIO_binmode(f,ptype,O_BINARY,":raw");
453 PerlIO_binmode(f,ptype,O_TEXT,":crlf");
455 On Unix these calls probably have no effect whatsoever.
456 Elsewhere they alter "\n" to CR,LF translation and possibly cause a special
457 text "end of file" indicator to be written or honoured on read. The effect of
458 making the call after doing any IO to the handle depends on the implementation. (It may be
459 ignored, affect any data which is already buffered as well, or only apply
462 =item PerlIO_debug(fmt,...)
464 PerlIO_debug is a printf()-like function which can be used for debugging.
465 No return value. Its main use is inside PerlIO where using real printf, warn() etc. would
466 recursively call PerlIO and be a problem.
468 PerlIO_debug writes to the file named by $ENV{'PERLIO_DEBUG'} typical use
473 PERLIO_DEBUG=/dev/tty ./perl somescript some args
476 setenv PERLIO_DEBUG /dev/tty
477 ./perl somescript some args
481 perl somescript some args
483 If $ENV{'PERLIO_DEBUG'} is not set PerlIO_debug() is a no-op.