| =head1 NAME |
| |
| perlapio - perl's IO abstraction interface. |
| |
| =head1 SYNOPSIS |
| |
| #define PERLIO_NOT_STDIO 0 /* For co-existence with stdio only */ |
| #include <perlio.h> /* Usually via #include <perl.h> */ |
| |
| PerlIO *PerlIO_stdin(void); |
| PerlIO *PerlIO_stdout(void); |
| PerlIO *PerlIO_stderr(void); |
| |
| PerlIO *PerlIO_open(const char *path,const char *mode); |
| PerlIO *PerlIO_fdopen(int fd, const char *mode); |
| PerlIO *PerlIO_reopen(const char *path, const char *mode, PerlIO *old); /* deprecated */ |
| int PerlIO_close(PerlIO *f); |
| |
| int PerlIO_stdoutf(const char *fmt,...) |
| int PerlIO_puts(PerlIO *f,const char *string); |
| int PerlIO_putc(PerlIO *f,int ch); |
| int PerlIO_write(PerlIO *f,const void *buf,size_t numbytes); |
| int PerlIO_printf(PerlIO *f, const char *fmt,...); |
| int PerlIO_vprintf(PerlIO *f, const char *fmt, va_list args); |
| int PerlIO_flush(PerlIO *f); |
| |
| int PerlIO_eof(PerlIO *f); |
| int PerlIO_error(PerlIO *f); |
| void PerlIO_clearerr(PerlIO *f); |
| |
| int PerlIO_getc(PerlIO *d); |
| int PerlIO_ungetc(PerlIO *f,int ch); |
| int PerlIO_read(PerlIO *f, void *buf, size_t numbytes); |
| |
| int PerlIO_fileno(PerlIO *f); |
| |
| void PerlIO_setlinebuf(PerlIO *f); |
| |
| Off_t PerlIO_tell(PerlIO *f); |
| int PerlIO_seek(PerlIO *f, Off_t offset, int whence); |
| void PerlIO_rewind(PerlIO *f); |
| |
| int PerlIO_getpos(PerlIO *f, SV *save); /* prototype changed */ |
| int PerlIO_setpos(PerlIO *f, SV *saved); /* prototype changed */ |
| |
| int PerlIO_fast_gets(PerlIO *f); |
| int PerlIO_has_cntptr(PerlIO *f); |
| int PerlIO_get_cnt(PerlIO *f); |
| char *PerlIO_get_ptr(PerlIO *f); |
| void PerlIO_set_ptrcnt(PerlIO *f, char *ptr, int count); |
| |
| int PerlIO_canset_cnt(PerlIO *f); /* deprecated */ |
| void PerlIO_set_cnt(PerlIO *f, int count); /* deprecated */ |
| |
| int PerlIO_has_base(PerlIO *f); |
| char *PerlIO_get_base(PerlIO *f); |
| int PerlIO_get_bufsiz(PerlIO *f); |
| |
| PerlIO *PerlIO_importFILE(FILE *stdio, const char *mode); |
| FILE *PerlIO_exportFILE(PerlIO *f, int flags); |
| FILE *PerlIO_findFILE(PerlIO *f); |
| void PerlIO_releaseFILE(PerlIO *f,FILE *stdio); |
| |
| int PerlIO_apply_layers(PerlIO *f, const char *mode, const char *layers); |
| int PerlIO_binmode(PerlIO *f, int ptype, int imode, const char *layers); |
| void PerlIO_debug(const char *fmt,...) |
| |
| =head1 DESCRIPTION |
| |
| Perl's source code, and extensions that want maximum portability, |
| should use the above functions instead of those defined in ANSI C's |
| I<stdio.h>. The perl headers (in particular "perlio.h") will |
| C<#define> them to the I/O mechanism selected at Configure time. |
| |
| The functions are modeled on those in I<stdio.h>, but parameter order |
| has been "tidied up a little". |
| |
| C<PerlIO *> takes the place of FILE *. Like FILE * it should be |
| treated as opaque (it is probably safe to assume it is a pointer to |
| something). |
| |
| There are currently three implementations: |
| |
| =over 4 |
| |
| =item 1. USE_STDIO |
| |
| All above are #define'd to stdio functions or are trivial wrapper |
| functions which call stdio. In this case I<only> PerlIO * is a FILE *. |
| This has been the default implementation since the abstraction was |
| introduced in perl5.003_02. |
| |
| =item 2. USE_SFIO |
| |
| A "legacy" implementation in terms of the "sfio" library. Used for |
| some specialist applications on Unix machines ("sfio" is not widely |
| ported away from Unix). Most of above are #define'd to the sfio |
| functions. PerlIO * is in this case Sfio_t *. |
| |
| =item 3. USE_PERLIO |
| |
| Introduced just after perl5.7.0, this is a re-implementation of the |
| above abstraction which allows perl more control over how IO is done |
| as it decouples IO from the way the operating system and C library |
| choose to do things. For USE_PERLIO PerlIO * has an extra layer of |
| indirection - it is a pointer-to-a-pointer. This allows the PerlIO * |
| to remain with a known value while swapping the implementation around |
| underneath I<at run time>. In this case all the above are true (but |
| very simple) functions which call the underlying implementation. |
| |
| This is the only implementation for which C<PerlIO_apply_layers()> |
| does anything "interesting". |
| |
| The USE_PERLIO implementation is described in L<perliol>. |
| |
| =back |
| |
| Because "perlio.h" is a thin layer (for efficiency) the semantics of |
| these functions are somewhat dependent on the underlying implementation. |
| Where these variations are understood they are noted below. |
| |
| Unless otherwise noted, functions return 0 on success, or a negative |
| value (usually C<EOF> which is usually -1) and set C<errno> on error. |
| |
| =over 4 |
| |
| =item B<PerlIO_stdin()>, B<PerlIO_stdout()>, B<PerlIO_stderr()> |
| |
| Use these rather than C<stdin>, C<stdout>, C<stderr>. They are written |
| to look like "function calls" rather than variables because this makes |
| it easier to I<make them> function calls if platform cannot export data |
| to loaded modules, or if (say) different "threads" might have different |
| values. |
| |
| =item B<PerlIO_open(path, mode)>, B<PerlIO_fdopen(fd,mode)> |
| |
| These correspond to fopen()/fdopen() and the arguments are the same. |
| Return C<NULL> and set C<errno> if there is an error. There may be an |
| implementation limit on the number of open handles, which may be lower |
| than the limit on the number of open files - C<errno> may not be set |
| when C<NULL> is returned if this limit is exceeded. |
| |
| =item B<PerlIO_reopen(path,mode,f)> |
| |
| While this currently exists in all three implementations perl itself |
| does not use it. I<As perl does not use it, it is not well tested.> |
| |
| Perl prefers to C<dup> the new low-level descriptor to the descriptor |
| used by the existing PerlIO. This may become the behaviour of this |
| function in the future. |
| |
| =item B<PerlIO_printf(f,fmt,...)>, B<PerlIO_vprintf(f,fmt,a)> |
| |
| These are fprintf()/vfprintf() equivalents. |
| |
| =item B<PerlIO_stdoutf(fmt,...)> |
| |
| This is printf() equivalent. printf is #defined to this function, |
| so it is (currently) legal to use C<printf(fmt,...)> in perl sources. |
| |
| =item B<PerlIO_read(f,buf,count)>, B<PerlIO_write(f,buf,count)> |
| |
| These correspond functionally to fread() and fwrite() but the |
| arguments and return values are different. The PerlIO_read() and |
| PerlIO_write() signatures have been modeled on the more sane low level |
| read() and write() functions instead: The "file" argument is passed |
| first, there is only one "count", and the return value can distinguish |
| between error and C<EOF>. |
| |
| Returns a byte count if successful (which may be zero or |
| positive), returns negative value and sets C<errno> on error. |
| Depending on implementation C<errno> may be C<EINTR> if operation was |
| interrupted by a signal. |
| |
| =item B<PerlIO_close(f)> |
| |
| Depending on implementation C<errno> may be C<EINTR> if operation was |
| interrupted by a signal. |
| |
| =item B<PerlIO_puts(f,s)>, B<PerlIO_putc(f,c)> |
| |
| These correspond to fputs() and fputc(). |
| Note that arguments have been revised to have "file" first. |
| |
| =item B<PerlIO_ungetc(f,c)> |
| |
| This corresponds to ungetc(). Note that arguments have been revised |
| to have "file" first. Arranges that next read operation will return |
| the byte B<c>. Despite the implied "character" in the name only |
| values in the range 0..0xFF are defined. Returns the byte B<c> on |
| success or -1 (C<EOF>) on error. The number of bytes that can be |
| "pushed back" may vary, only 1 character is certain, and then only if |
| it is the last character that was read from the handle. |
| |
| =item B<PerlIO_getc(f)> |
| |
| This corresponds to getc(). |
| Despite the c in the name only byte range 0..0xFF is supported. |
| Returns the character read or -1 (C<EOF>) on error. |
| |
| =item B<PerlIO_eof(f)> |
| |
| This corresponds to feof(). Returns a true/false indication of |
| whether the handle is at end of file. For terminal devices this may |
| or may not be "sticky" depending on the implementation. The flag is |
| cleared by PerlIO_seek(), or PerlIO_rewind(). |
| |
| =item B<PerlIO_error(f)> |
| |
| This corresponds to ferror(). Returns a true/false indication of |
| whether there has been an IO error on the handle. |
| |
| =item B<PerlIO_fileno(f)> |
| |
| This corresponds to fileno(), note that on some platforms, the meaning |
| of "fileno" may not match Unix. Returns -1 if the handle has no open |
| descriptor associated with it. |
| |
| =item B<PerlIO_clearerr(f)> |
| |
| This corresponds to clearerr(), i.e., clears 'error' and (usually) |
| 'eof' flags for the "stream". Does not return a value. |
| |
| =item B<PerlIO_flush(f)> |
| |
| This corresponds to fflush(). Sends any buffered write data to the |
| underlying file. If called with C<NULL> this may flush all open |
| streams (or core dump with some USE_STDIO implementations). Calling |
| on a handle open for read only, or on which last operation was a read |
| of some kind may lead to undefined behaviour on some USE_STDIO |
| implementations. The USE_PERLIO (layers) implementation tries to |
| behave better: it flushes all open streams when passed C<NULL>, and |
| attempts to retain data on read streams either in the buffer or by |
| seeking the handle to the current logical position. |
| |
| =item B<PerlIO_seek(f,offset,whence)> |
| |
| This corresponds to fseek(). Sends buffered write data to the |
| underlying file, or discards any buffered read data, then positions |
| the file descriptor as specified by B<offset> and B<whence> (sic). |
| This is the correct thing to do when switching between read and write |
| on the same handle (see issues with PerlIO_flush() above). Offset is |
| of type C<Off_t> which is a perl Configure value which may not be same |
| as stdio's C<off_t>. |
| |
| =item B<PerlIO_tell(f)> |
| |
| This corresponds to ftell(). Returns the current file position, or |
| (Off_t) -1 on error. May just return value system "knows" without |
| making a system call or checking the underlying file descriptor (so |
| use on shared file descriptors is not safe without a |
| PerlIO_seek()). Return value is of type C<Off_t> which is a perl |
| Configure value which may not be same as stdio's C<off_t>. |
| |
| =item B<PerlIO_getpos(f,p)>, B<PerlIO_setpos(f,p)> |
| |
| These correspond (loosely) to fgetpos() and fsetpos(). Rather than |
| stdio's Fpos_t they expect a "Perl Scalar Value" to be passed. What is |
| stored there should be considered opaque. The layout of the data may |
| vary from handle to handle. When not using stdio or if platform does |
| not have the stdio calls then they are implemented in terms of |
| PerlIO_tell() and PerlIO_seek(). |
| |
| =item B<PerlIO_rewind(f)> |
| |
| This corresponds to rewind(). It is usually defined as being |
| |
| PerlIO_seek(f,(Off_t)0L, SEEK_SET); |
| PerlIO_clearerr(f); |
| |
| =item B<PerlIO_tmpfile()> |
| |
| This corresponds to tmpfile(), i.e., returns an anonymous PerlIO or |
| NULL on error. The system will attempt to automatically delete the |
| file when closed. On Unix the file is usually C<unlink>-ed just after |
| it is created so it does not matter how it gets closed. On other |
| systems the file may only be deleted if closed via PerlIO_close() |
| and/or the program exits via C<exit>. Depending on the implementation |
| there may be "race conditions" which allow other processes access to |
| the file, though in general it will be safer in this regard than |
| ad. hoc. schemes. |
| |
| =item B<PerlIO_setlinebuf(f)> |
| |
| This corresponds to setlinebuf(). Does not return a value. What |
| constitutes a "line" is implementation dependent but usually means |
| that writing "\n" flushes the buffer. What happens with things like |
| "this\nthat" is uncertain. (Perl core uses it I<only> when "dumping"; |
| it has nothing to do with $| auto-flush.) |
| |
| =back |
| |
| =head2 Co-existence with stdio |
| |
| There is outline support for co-existence of PerlIO with stdio. |
| Obviously if PerlIO is implemented in terms of stdio there is no |
| problem. However in other cases then mechanisms must exist to create a |
| FILE * which can be passed to library code which is going to use stdio |
| calls. |
| |
| The first step is to add this line: |
| |
| #define PERLIO_NOT_STDIO 0 |
| |
| I<before> including any perl header files. (This will probably become |
| the default at some point). That prevents "perlio.h" from attempting |
| to #define stdio functions onto PerlIO functions. |
| |
| XS code is probably better using "typemap" if it expects FILE * |
| arguments. The standard typemap will be adjusted to comprehend any |
| changes in this area. |
| |
| =over 4 |
| |
| =item B<PerlIO_importFILE(f,mode)> |
| |
| Used to get a PerlIO * from a FILE *. |
| |
| The mode argument should be a string as would be passed to |
| fopen/PerlIO_open. If it is NULL then - for legacy support - the code |
| will (depending upon the platform and the implementation) either |
| attempt to empirically determine the mode in which I<f> is open, or |
| use "r+" to indicate a read/write stream. |
| |
| Once called the FILE * should I<ONLY> be closed by calling |
| C<PerlIO_close()> on the returned PerlIO *. |
| |
| The PerlIO is set to textmode. Use PerlIO_binmode if this is |
| not the desired mode. |
| |
| This is B<not> the reverse of PerlIO_exportFILE(). |
| |
| =item B<PerlIO_exportFILE(f,mode)> |
| |
| Given a PerlIO * create a 'native' FILE * suitable for passing to code |
| expecting to be compiled and linked with ANSI C I<stdio.h>. The mode |
| argument should be a string as would be passed to fopen/PerlIO_open. |
| If it is NULL then - for legacy support - the FILE * is opened in same |
| mode as the PerlIO *. |
| |
| The fact that such a FILE * has been 'exported' is recorded, (normally |
| by pushing a new :stdio "layer" onto the PerlIO *), which may affect |
| future PerlIO operations on the original PerlIO *. You should not |
| call C<fclose()> on the file unless you call C<PerlIO_releaseFILE()> |
| to disassociate it from the PerlIO *. (Do not use PerlIO_importFILE() |
| for doing the disassociation.) |
| |
| Calling this function repeatedly will create a FILE * on each call |
| (and will push an :stdio layer each time as well). |
| |
| =item B<PerlIO_releaseFILE(p,f)> |
| |
| Calling PerlIO_releaseFILE informs PerlIO that all use of FILE * is |
| complete. It is removed from the list of 'exported' FILE *s, and the |
| associated PerlIO * should revert to its original behaviour. |
| |
| Use this to disassociate a file from a PerlIO * that was associated |
| using PerlIO_exportFILE(). |
| |
| =item B<PerlIO_findFILE(f)> |
| |
| Returns a native FILE * used by a stdio layer. If there is none, it |
| will create one with PerlIO_exportFILE. In either case the FILE * |
| should be considered as belonging to PerlIO subsystem and should |
| only be closed by calling C<PerlIO_close()>. |
| |
| |
| =back |
| |
| =head2 "Fast gets" Functions |
| |
| In addition to standard-like API defined so far above there is an |
| "implementation" interface which allows perl to get at internals of |
| PerlIO. The following calls correspond to the various FILE_xxx macros |
| determined by Configure - or their equivalent in other |
| implementations. This section is really of interest to only those |
| concerned with detailed perl-core behaviour, implementing a PerlIO |
| mapping or writing code which can make use of the "read ahead" that |
| has been done by the IO system in the same way perl does. Note that |
| any code that uses these interfaces must be prepared to do things the |
| traditional way if a handle does not support them. |
| |
| =over 4 |
| |
| =item B<PerlIO_fast_gets(f)> |
| |
| Returns true if implementation has all the interfaces required to |
| allow perl's C<sv_gets> to "bypass" normal IO mechanism. This can |
| vary from handle to handle. |
| |
| PerlIO_fast_gets(f) = PerlIO_has_cntptr(f) && \ |
| PerlIO_canset_cnt(f) && \ |
| 'Can set pointer into buffer' |
| |
| =item B<PerlIO_has_cntptr(f)> |
| |
| Implementation can return pointer to current position in the "buffer" |
| and a count of bytes available in the buffer. Do not use this - use |
| PerlIO_fast_gets. |
| |
| =item B<PerlIO_get_cnt(f)> |
| |
| Return count of readable bytes in the buffer. Zero or negative return |
| means no more bytes available. |
| |
| =item B<PerlIO_get_ptr(f)> |
| |
| Return pointer to next readable byte in buffer, accessing via the |
| pointer (dereferencing) is only safe if PerlIO_get_cnt() has returned |
| a positive value. Only positive offsets up to value returned by |
| PerlIO_get_cnt() are allowed. |
| |
| =item B<PerlIO_set_ptrcnt(f,p,c)> |
| |
| Set pointer into buffer, and a count of bytes still in the |
| buffer. Should be used only to set pointer to within range implied by |
| previous calls to C<PerlIO_get_ptr> and C<PerlIO_get_cnt>. The two |
| values I<must> be consistent with each other (implementation may only |
| use one or the other or may require both). |
| |
| =item B<PerlIO_canset_cnt(f)> |
| |
| Implementation can adjust its idea of number of bytes in the buffer. |
| Do not use this - use PerlIO_fast_gets. |
| |
| =item B<PerlIO_set_cnt(f,c)> |
| |
| Obscure - set count of bytes in the buffer. Deprecated. Only usable |
| if PerlIO_canset_cnt() returns true. Currently used in only doio.c to |
| force count less than -1 to -1. Perhaps should be PerlIO_set_empty or |
| similar. This call may actually do nothing if "count" is deduced from |
| pointer and a "limit". Do not use this - use PerlIO_set_ptrcnt(). |
| |
| =item B<PerlIO_has_base(f)> |
| |
| Returns true if implementation has a buffer, and can return pointer |
| to whole buffer and its size. Used by perl for B<-T> / B<-B> tests. |
| Other uses would be very obscure... |
| |
| =item B<PerlIO_get_base(f)> |
| |
| Return I<start> of buffer. Access only positive offsets in the buffer |
| up to the value returned by PerlIO_get_bufsiz(). |
| |
| =item B<PerlIO_get_bufsiz(f)> |
| |
| Return the I<total number of bytes> in the buffer, this is neither the |
| number that can be read, nor the amount of memory allocated to the |
| buffer. Rather it is what the operating system and/or implementation |
| happened to C<read()> (or whatever) last time IO was requested. |
| |
| =back |
| |
| =head2 Other Functions |
| |
| =over 4 |
| |
| =item PerlIO_apply_layers(f,mode,layers) |
| |
| The new interface to the USE_PERLIO implementation. The layers ":crlf" |
| and ":raw" are only ones allowed for other implementations and those |
| are silently ignored. (As of perl5.8 ":raw" is deprecated.) Use |
| PerlIO_binmode() below for the portable case. |
| |
| =item PerlIO_binmode(f,ptype,imode,layers) |
| |
| The hook used by perl's C<binmode> operator. |
| B<ptype> is perl's character for the kind of IO: |
| |
| =over 8 |
| |
| =item 'E<lt>' read |
| |
| =item 'E<gt>' write |
| |
| =item '+' read/write |
| |
| =back |
| |
| B<imode> is C<O_BINARY> or C<O_TEXT>. |
| |
| B<layers> is a string of layers to apply, only ":crlf" makes sense in |
| the non USE_PERLIO case. (As of perl5.8 ":raw" is deprecated in favour |
| of passing NULL.) |
| |
| Portable cases are: |
| |
| PerlIO_binmode(f,ptype,O_BINARY,NULL); |
| and |
| PerlIO_binmode(f,ptype,O_TEXT,":crlf"); |
| |
| On Unix these calls probably have no effect whatsoever. Elsewhere |
| they alter "\n" to CR,LF translation and possibly cause a special text |
| "end of file" indicator to be written or honoured on read. The effect |
| of making the call after doing any IO to the handle depends on the |
| implementation. (It may be ignored, affect any data which is already |
| buffered as well, or only apply to subsequent data.) |
| |
| =item PerlIO_debug(fmt,...) |
| |
| PerlIO_debug is a printf()-like function which can be used for |
| debugging. No return value. Its main use is inside PerlIO where using |
| real printf, warn() etc. would recursively call PerlIO and be a |
| problem. |
| |
| PerlIO_debug writes to the file named by $ENV{'PERLIO_DEBUG'} typical |
| use might be |
| |
| Bourne shells (sh, ksh, bash, zsh, ash, ...): |
| PERLIO_DEBUG=/dev/tty ./perl somescript some args |
| |
| Csh/Tcsh: |
| setenv PERLIO_DEBUG /dev/tty |
| ./perl somescript some args |
| |
| If you have the "env" utility: |
| env PERLIO_DEBUG=/dev/tty ./perl somescript some args |
| |
| Win32: |
| set PERLIO_DEBUG=CON |
| perl somescript some args |
| |
| If $ENV{'PERLIO_DEBUG'} is not set PerlIO_debug() is a no-op. |
| |
| =back |