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   1  =head1 NAME
   2  
   3  perlapio - perl's IO abstraction interface.
   4  
   5  =head1 SYNOPSIS
   6  
   7      #define PERLIO_NOT_STDIO 0    /* For co-existence with stdio only */
   8      #include <perlio.h>           /* Usually via #include <perl.h> */
   9  
  10      PerlIO *PerlIO_stdin(void);
  11      PerlIO *PerlIO_stdout(void);
  12      PerlIO *PerlIO_stderr(void);
  13  
  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  
  59      PerlIO *PerlIO_importFILE(FILE *stdio, const char *mode);
  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,...)
  67  
  68  =head1 DESCRIPTION
  69  
  70  Perl's source code, and extensions that want maximum portability,
  71  should use the above functions instead of those defined in ANSI C's
  72  I<stdio.h>.  The perl headers (in particular "perlio.h") will
  73  C<#define> them to the I/O mechanism selected at Configure time.
  74  
  75  The functions are modeled on those in I<stdio.h>, but parameter order
  76  has been "tidied up a little".
  77  
  78  C<PerlIO *> takes the place of FILE *. Like FILE * it should be
  79  treated as opaque (it is probably safe to assume it is a pointer to
  80  something).
  81  
  82  There are currently three implementations:
  83  
  84  =over 4
  85  
  86  =item 1. USE_STDIO
  87  
  88  All above are #define'd to stdio functions or are trivial wrapper
  89  functions which call stdio. In this case I<only> PerlIO * is a FILE *.
  90  This has been the default implementation since the abstraction was
  91  introduced in perl5.003_02.
  92  
  93  =item 2. USE_SFIO
  94  
  95  A "legacy" implementation in terms of the "sfio" library. Used for
  96  some specialist applications on Unix machines ("sfio" is not widely
  97  ported away from Unix).  Most of above are #define'd to the sfio
  98  functions. PerlIO * is in this case Sfio_t *.
  99  
 100  =item 3. USE_PERLIO
 101  
 102  Introduced just after perl5.7.0, this is a re-implementation of the
 103  above abstraction which allows perl more control over how IO is done
 104  as it decouples IO from the way the operating system and C library
 105  choose to do things. For USE_PERLIO PerlIO * has an extra layer of
 106  indirection - it is a pointer-to-a-pointer.  This allows the PerlIO *
 107  to remain with a known value while swapping the implementation around
 108  underneath I<at run time>. In this case all the above are true (but
 109  very simple) functions which call the underlying implementation.
 110  
 111  This is the only implementation for which C<PerlIO_apply_layers()>
 112  does anything "interesting".
 113  
 114  The USE_PERLIO implementation is described in L<perliol>.
 115  
 116  =back
 117  
 118  Because "perlio.h" is a thin layer (for efficiency) the semantics of
 119  these functions are somewhat dependent on the underlying implementation.
 120  Where these variations are understood they are noted below.
 121  
 122  Unless otherwise noted, functions return 0 on success, or a negative
 123  value (usually C<EOF> which is usually -1) and set C<errno> on error.
 124  
 125  =over 4
 126  
 127  =item B<PerlIO_stdin()>, B<PerlIO_stdout()>, B<PerlIO_stderr()>
 128  
 129  Use these rather than C<stdin>, C<stdout>, C<stderr>. They are written
 130  to look like "function calls" rather than variables because this makes
 131  it easier to I<make them> function calls if platform cannot export data
 132  to loaded modules, or if (say) different "threads" might have different
 133  values.
 134  
 135  =item B<PerlIO_open(path, mode)>, B<PerlIO_fdopen(fd,mode)>
 136  
 137  These correspond to fopen()/fdopen() and the arguments are the same.
 138  Return C<NULL> and set C<errno> if there is an error.  There may be an
 139  implementation limit on the number of open handles, which may be lower
 140  than the limit on the number of open files - C<errno> may not be set
 141  when C<NULL> is returned if this limit is exceeded.
 142  
 143  =item B<PerlIO_reopen(path,mode,f)>
 144  
 145  While this currently exists in all three implementations perl itself
 146  does not use it. I<As perl does not use it, it is not well tested.>
 147  
 148  Perl prefers to C<dup> the new low-level descriptor to the descriptor
 149  used by the existing PerlIO. This may become the behaviour of this
 150  function in the future.
 151  
 152  =item B<PerlIO_printf(f,fmt,...)>, B<PerlIO_vprintf(f,fmt,a)>
 153  
 154  These are fprintf()/vfprintf() equivalents.
 155  
 156  =item B<PerlIO_stdoutf(fmt,...)>
 157  
 158  This is printf() equivalent. printf is #defined to this function,
 159  so it is (currently) legal to use C<printf(fmt,...)> in perl sources.
 160  
 161  =item B<PerlIO_read(f,buf,count)>, B<PerlIO_write(f,buf,count)>
 162  
 163  These correspond functionally to fread() and fwrite() but the
 164  arguments and return values are different.  The PerlIO_read() and
 165  PerlIO_write() signatures have been modeled on the more sane low level
 166  read() and write() functions instead: The "file" argument is passed
 167  first, there is only one "count", and the return value can distinguish
 168  between error and C<EOF>.
 169  
 170  Returns a byte count if successful (which may be zero or
 171  positive), returns negative value and sets C<errno> on error.
 172  Depending on implementation C<errno> may be C<EINTR> if operation was
 173  interrupted by a signal.
 174  
 175  =item B<PerlIO_close(f)>
 176  
 177  Depending on implementation C<errno> may be C<EINTR> if operation was
 178  interrupted by a signal.
 179  
 180  =item B<PerlIO_puts(f,s)>, B<PerlIO_putc(f,c)>
 181  
 182  These correspond to fputs() and fputc().
 183  Note that arguments have been revised to have "file" first.
 184  
 185  =item B<PerlIO_ungetc(f,c)>
 186  
 187  This corresponds to ungetc().  Note that arguments have been revised
 188  to have "file" first.  Arranges that next read operation will return
 189  the byte B<c>.  Despite the implied "character" in the name only
 190  values in the range 0..0xFF are defined. Returns the byte B<c> on
 191  success 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
 193  it is the last character that was read from the handle.
 194  
 195  =item B<PerlIO_getc(f)>
 196  
 197  This corresponds to getc().
 198  Despite the c in the name only byte range 0..0xFF is supported.
 199  Returns the character read or -1 (C<EOF>) on error.
 200  
 201  =item B<PerlIO_eof(f)>
 202  
 203  This corresponds to feof().  Returns a true/false indication of
 204  whether the handle is at end of file.  For terminal devices this may
 205  or may not be "sticky" depending on the implementation.  The flag is
 206  cleared by PerlIO_seek(), or PerlIO_rewind().
 207  
 208  =item B<PerlIO_error(f)>
 209  
 210  This corresponds to ferror().  Returns a true/false indication of
 211  whether there has been an IO error on the handle.
 212  
 213  =item B<PerlIO_fileno(f)>
 214  
 215  This corresponds to fileno(), note that on some platforms, the meaning
 216  of "fileno" may not match Unix. Returns -1 if the handle has no open
 217  descriptor associated with it.
 218  
 219  =item B<PerlIO_clearerr(f)>
 220  
 221  This corresponds to clearerr(), i.e., clears 'error' and (usually)
 222  'eof' flags for the "stream". Does not return a value.
 223  
 224  =item B<PerlIO_flush(f)>
 225  
 226  This corresponds to fflush().  Sends any buffered write data to the
 227  underlying file.  If called with C<NULL> this may flush all open
 228  streams (or core dump with some USE_STDIO implementations).  Calling
 229  on a handle open for read only, or on which last operation was a read
 230  of some kind may lead to undefined behaviour on some USE_STDIO
 231  implementations.  The USE_PERLIO (layers) implementation tries to
 232  behave better: it flushes all open streams when passed C<NULL>, and
 233  attempts to retain data on read streams either in the buffer or by
 234  seeking the handle to the current logical position.
 235  
 236  =item B<PerlIO_seek(f,offset,whence)>
 237  
 238  This corresponds to fseek().  Sends buffered write data to the
 239  underlying file, or discards any buffered read data, then positions
 240  the file descriptor as specified by B<offset> and B<whence> (sic).
 241  This is the correct thing to do when switching between read and write
 242  on the same handle (see issues with PerlIO_flush() above).  Offset is
 243  of type C<Off_t> which is a perl Configure value which may not be same
 244  as stdio's C<off_t>.
 245  
 246  =item B<PerlIO_tell(f)>
 247  
 248  This corresponds to ftell().  Returns the current file position, or
 249  (Off_t) -1 on error.  May just return value system "knows" without
 250  making a system call or checking the underlying file descriptor (so
 251  use on shared file descriptors is not safe without a
 252  PerlIO_seek()). Return value is of type C<Off_t> which is a perl
 253  Configure value which may not be same as stdio's C<off_t>.
 254  
 255  =item B<PerlIO_getpos(f,p)>, B<PerlIO_setpos(f,p)>
 256  
 257  These correspond (loosely) to fgetpos() and fsetpos(). Rather than
 258  stdio's Fpos_t they expect a "Perl Scalar Value" to be passed. What is
 259  stored there should be considered opaque. The layout of the data may
 260  vary from handle to handle.  When not using stdio or if platform does
 261  not have the stdio calls then they are implemented in terms of
 262  PerlIO_tell() and PerlIO_seek().
 263  
 264  =item B<PerlIO_rewind(f)>
 265  
 266  This corresponds to rewind(). It is usually defined as being
 267  
 268      PerlIO_seek(f,(Off_t)0L, SEEK_SET);
 269      PerlIO_clearerr(f);
 270  
 271  =item B<PerlIO_tmpfile()>
 272  
 273  This corresponds to tmpfile(), i.e., returns an anonymous PerlIO or
 274  NULL on error.  The system will attempt to automatically delete the
 275  file when closed.  On Unix the file is usually C<unlink>-ed just after
 276  it is created so it does not matter how it gets closed. On other
 277  systems the file may only be deleted if closed via PerlIO_close()
 278  and/or the program exits via C<exit>.  Depending on the implementation
 279  there may be "race conditions" which allow other processes access to
 280  the file, though in general it will be safer in this regard than
 281  ad. hoc. schemes.
 282  
 283  =item B<PerlIO_setlinebuf(f)>
 284  
 285  This corresponds to setlinebuf().  Does not return a value. What
 286  constitutes a "line" is implementation dependent but usually means
 287  that writing "\n" flushes the buffer.  What happens with things like
 288  "this\nthat" is uncertain.  (Perl core uses it I<only> when "dumping";
 289  it has nothing to do with $| auto-flush.)
 290  
 291  =back
 292  
 293  =head2 Co-existence with stdio
 294  
 295  There is outline support for co-existence of PerlIO with stdio.
 296  Obviously if PerlIO is implemented in terms of stdio there is no
 297  problem. However in other cases then mechanisms must exist to create a
 298  FILE * which can be passed to library code which is going to use stdio
 299  calls.
 300  
 301  The first step is to add this line:
 302  
 303     #define PERLIO_NOT_STDIO 0
 304  
 305  I<before> including any perl header files. (This will probably become
 306  the default at some point).  That prevents "perlio.h" from attempting
 307  to #define stdio functions onto PerlIO functions.
 308  
 309  XS code is probably better using "typemap" if it expects FILE *
 310  arguments.  The standard typemap will be adjusted to comprehend any
 311  changes in this area.
 312  
 313  =over 4
 314  
 315  =item B<PerlIO_importFILE(f,mode)>
 316  
 317  Used to get a PerlIO * from a FILE *.
 318  
 319  The mode argument should be a string as would be passed to
 320  fopen/PerlIO_open.  If it is NULL then - for legacy support - the code
 321  will (depending upon the platform and the implementation) either
 322  attempt to empirically determine the mode in which I<f> is open, or
 323  use "r+" to indicate a read/write stream.
 324  
 325  Once called the FILE * should I<ONLY> be closed by calling
 326  C<PerlIO_close()> on the returned PerlIO *.
 327  
 328  The PerlIO is set to textmode. Use PerlIO_binmode if this is
 329  not the desired mode.
 330  
 331  This is B<not> the reverse of PerlIO_exportFILE().
 332  
 333  =item B<PerlIO_exportFILE(f,mode)>
 334  
 335  Given a PerlIO * create a 'native' FILE * suitable for passing to code
 336  expecting to be compiled and linked with ANSI C I<stdio.h>.  The mode
 337  argument should be a string as would be passed to fopen/PerlIO_open.
 338  If it is NULL then - for legacy support - the FILE * is opened in same
 339  mode as the PerlIO *.
 340  
 341  The fact that such a FILE * has been 'exported' is recorded, (normally
 342  by pushing a new :stdio "layer" onto the PerlIO *), which may affect
 343  future PerlIO operations on the original PerlIO *.  You should not
 344  call C<fclose()> on the file unless you call C<PerlIO_releaseFILE()>
 345  to disassociate it from the PerlIO *.  (Do not use PerlIO_importFILE()
 346  for doing the disassociation.)
 347  
 348  Calling this function repeatedly will create a FILE * on each call
 349  (and will push an :stdio layer each time as well).
 350  
 351  =item B<PerlIO_releaseFILE(p,f)>
 352  
 353  Calling PerlIO_releaseFILE informs PerlIO that all use of FILE * is
 354  complete. It is removed from the list of 'exported' FILE *s, and the
 355  associated PerlIO * should revert to its original behaviour.
 356  
 357  Use this to disassociate a file from a PerlIO * that was associated
 358  using PerlIO_exportFILE().
 359  
 360  =item B<PerlIO_findFILE(f)>
 361  
 362  Returns a native FILE * used by a stdio layer. If there is none, it
 363  will create one with PerlIO_exportFILE. In either case the FILE *
 364  should be considered as belonging to PerlIO subsystem and should
 365  only be closed by calling C<PerlIO_close()>.
 366  
 367  
 368  =back
 369  
 370  =head2 "Fast gets" Functions
 371  
 372  In addition to standard-like API defined so far above there is an
 373  "implementation" interface which allows perl to get at internals of
 374  PerlIO.  The following calls correspond to the various FILE_xxx macros
 375  determined by Configure - or their equivalent in other
 376  implementations. This section is really of interest to only those
 377  concerned with detailed perl-core behaviour, implementing a PerlIO
 378  mapping or writing code which can make use of the "read ahead" that
 379  has been done by the IO system in the same way perl does. Note that
 380  any code that uses these interfaces must be prepared to do things the
 381  traditional way if a handle does not support them.
 382  
 383  =over 4
 384  
 385  =item B<PerlIO_fast_gets(f)>
 386  
 387  Returns true if implementation has all the interfaces required to
 388  allow perl's C<sv_gets> to "bypass" normal IO mechanism.  This can
 389  vary from handle to handle.
 390  
 391    PerlIO_fast_gets(f) = PerlIO_has_cntptr(f) && \
 392                          PerlIO_canset_cnt(f) && \
 393                          `Can set pointer into buffer'
 394  
 395  
 396  =item B<PerlIO_has_cntptr(f)>
 397  
 398  Implementation can return pointer to current position in the "buffer"
 399  and a count of bytes available in the buffer.  Do not use this - use
 400  PerlIO_fast_gets.
 401  
 402  =item B<PerlIO_get_cnt(f)>
 403  
 404  Return count of readable bytes in the buffer. Zero or negative return
 405  means no more bytes available.
 406  
 407  =item B<PerlIO_get_ptr(f)>
 408  
 409  Return pointer to next readable byte in buffer, accessing via the
 410  pointer (dereferencing) is only safe if PerlIO_get_cnt() has returned
 411  a positive value.  Only positive offsets up to value returned by
 412  PerlIO_get_cnt() are allowed.
 413  
 414  =item B<PerlIO_set_ptrcnt(f,p,c)>
 415  
 416  Set pointer into buffer, and a count of bytes still in the
 417  buffer. Should be used only to set pointer to within range implied by
 418  previous calls to C<PerlIO_get_ptr> and C<PerlIO_get_cnt>. The two
 419  values I<must> be consistent with each other (implementation may only
 420  use one or the other or may require both).
 421  
 422  =item B<PerlIO_canset_cnt(f)>
 423  
 424  Implementation can adjust its idea of number of bytes in the buffer.
 425  Do not use this - use PerlIO_fast_gets.
 426  
 427  =item B<PerlIO_set_cnt(f,c)>
 428  
 429  Obscure - set count of bytes in the buffer. Deprecated.  Only usable
 430  if PerlIO_canset_cnt() returns true.  Currently used in only doio.c to
 431  force count less than -1 to -1.  Perhaps should be PerlIO_set_empty or
 432  similar.  This call may actually do nothing if "count" is deduced from
 433  pointer and a "limit".  Do not use this - use PerlIO_set_ptrcnt().
 434  
 435  =item B<PerlIO_has_base(f)>
 436  
 437  Returns true if implementation has a buffer, and can return pointer
 438  to whole buffer and its size. Used by perl for B<-T> / B<-B> tests.
 439  Other uses would be very obscure...
 440  
 441  =item B<PerlIO_get_base(f)>
 442  
 443  Return I<start> of buffer. Access only positive offsets in the buffer
 444  up to the value returned by PerlIO_get_bufsiz().
 445  
 446  =item B<PerlIO_get_bufsiz(f)>
 447  
 448  Return the I<total number of bytes> in the buffer, this is neither the
 449  number that can be read, nor the amount of memory allocated to the
 450  buffer. Rather it is what the operating system and/or implementation
 451  happened to C<read()> (or whatever) last time IO was requested.
 452  
 453  =back
 454  
 455  =head2 Other Functions
 456  
 457  =over 4
 458  
 459  =item PerlIO_apply_layers(f,mode,layers)
 460  
 461  The new interface to the USE_PERLIO implementation. The layers ":crlf"
 462  and ":raw" are only ones allowed for other implementations and those
 463  are silently ignored. (As of perl5.8 ":raw" is deprecated.)  Use
 464  PerlIO_binmode() below for the portable case.
 465  
 466  =item PerlIO_binmode(f,ptype,imode,layers)
 467  
 468  The hook used by perl's C<binmode> operator.
 469  B<ptype> is perl's character for the kind of IO:
 470  
 471  =over 8
 472  
 473  =item 'E<lt>' read
 474  
 475  =item 'E<gt>' write
 476  
 477  =item '+' read/write
 478  
 479  =back
 480  
 481  B<imode> is C<O_BINARY> or C<O_TEXT>.
 482  
 483  B<layers> is a string of layers to apply, only ":crlf" makes sense in
 484  the non USE_PERLIO case. (As of perl5.8 ":raw" is deprecated in favour
 485  of passing NULL.)
 486  
 487  Portable cases are:
 488  
 489      PerlIO_binmode(f,ptype,O_BINARY,Nullch);
 490  and
 491      PerlIO_binmode(f,ptype,O_TEXT,":crlf");
 492  
 493  On Unix these calls probably have no effect whatsoever.  Elsewhere
 494  they 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
 496  of making the call after doing any IO to the handle depends on the
 497  implementation. (It may be ignored, affect any data which is already
 498  buffered as well, or only apply to subsequent data.)
 499  
 500  =item PerlIO_debug(fmt,...)
 501  
 502  PerlIO_debug is a printf()-like function which can be used for
 503  debugging.  No return value. Its main use is inside PerlIO where using
 504  real printf, warn() etc. would recursively call PerlIO and be a
 505  problem.
 506  
 507  PerlIO_debug writes to the file named by $ENV{'PERLIO_DEBUG'} typical
 508  use might be
 509  
 510    Bourne shells (sh, ksh, bash, zsh, ash, ...):
 511     PERLIO_DEBUG=/dev/tty ./perl somescript some args
 512  
 513    Csh/Tcsh:
 514     setenv PERLIO_DEBUG /dev/tty
 515     ./perl somescript some args
 516  
 517    If you have the "env" utility:
 518     env PERLIO_DEBUG=/dev/tty ./perl somescript some args
 519  
 520    Win32:
 521     set PERLIO_DEBUG=CON
 522     perl somescript some args
 523  
 524  If $ENV{'PERLIO_DEBUG'} is not set PerlIO_debug() is a no-op.
 525  
 526  =back