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Diffstat (limited to 'Master/tlpkg/tlperl/lib/pods/perlapio.pod')
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diff --git a/Master/tlpkg/tlperl/lib/pods/perlapio.pod b/Master/tlpkg/tlperl/lib/pods/perlapio.pod new file mode 100644 index 00000000000..1c57f9a9a89 --- /dev/null +++ b/Master/tlpkg/tlperl/lib/pods/perlapio.pod @@ -0,0 +1,526 @@ +=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 |