X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperlapio.pod;h=06e3d14e62d1c6b35dca36299bb2b666f2fc8a91;hb=0c8d858bc5dbd18f38dfa055bba011a276ec0bb8;hp=f69e79502ccaa69d5310186b74b12ad5c9105f9b;hpb=7b8d334a971230040a212bc5038097b3f600a094;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perlapio.pod b/pod/perlapio.pod index f69e795..06e3d14 100644 --- a/pod/perlapio.pod +++ b/pod/perlapio.pod @@ -4,71 +4,121 @@ perlapio - perl's IO abstraction interface. =head1 SYNOPSIS + #define PERLIO_NOT_STDIO 0 /* For co-existence with stdio only */ + #include /* Usually via #include */ + PerlIO *PerlIO_stdin(void); PerlIO *PerlIO_stdout(void); PerlIO *PerlIO_stderr(void); - PerlIO *PerlIO_open(const char *,const char *); - int PerlIO_close(PerlIO *); - - int PerlIO_stdoutf(const char *,...) - int PerlIO_puts(PerlIO *,const char *); - int PerlIO_putc(PerlIO *,int); - int PerlIO_write(PerlIO *,const void *,size_t); - int PerlIO_printf(PerlIO *, const char *,...); - int PerlIO_vprintf(PerlIO *, const char *, va_list); - int PerlIO_flush(PerlIO *); - - int PerlIO_eof(PerlIO *); - int PerlIO_error(PerlIO *); - void PerlIO_clearerr(PerlIO *); - - int PerlIO_getc(PerlIO *); - int PerlIO_ungetc(PerlIO *,int); - int PerlIO_read(PerlIO *,void *,size_t); - - int PerlIO_fileno(PerlIO *); - PerlIO *PerlIO_fdopen(int, const char *); - PerlIO *PerlIO_importFILE(FILE *, int flags); - FILE *PerlIO_exportFILE(PerlIO *, int flags); - FILE *PerlIO_findFILE(PerlIO *); - void PerlIO_releaseFILE(PerlIO *,FILE *); - - void PerlIO_setlinebuf(PerlIO *); - - long PerlIO_tell(PerlIO *); - int PerlIO_seek(PerlIO *,off_t,int); - int PerlIO_getpos(PerlIO *,Fpos_t *) - int PerlIO_setpos(PerlIO *,Fpos_t *) - void PerlIO_rewind(PerlIO *); - - int PerlIO_has_base(PerlIO *); - int PerlIO_has_cntptr(PerlIO *); - int PerlIO_fast_gets(PerlIO *); - int PerlIO_canset_cnt(PerlIO *); - - char *PerlIO_get_ptr(PerlIO *); - int PerlIO_get_cnt(PerlIO *); - void PerlIO_set_cnt(PerlIO *,int); - void PerlIO_set_ptrcnt(PerlIO *,char *,int); - char *PerlIO_get_base(PerlIO *); - int PerlIO_get_bufsiz(PerlIO *); + 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, int flags); + 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 should use the above functions instead of those -defined in ANSI C's I, I will the C<#define> them to -the I/O mechanism selected at Configure time. +Perl's source code, and extensions that want maximum portability, should use the above +functions instead of those defined in ANSI C's I. 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, but parameter order has been "tidied up a little". +C 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 B +=item 1. USE_STDIO -This 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). +All above are #define'd to stdio functions or are trivial wrapper functions which +call stdio. In this case I 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 arround underneath I. 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 does anything +"interesting". + +The USE_PERLIO implementation is described in L. + +=back + +Because "perlio.h" is a thing layer (for efficiency) the semantics of these functions are +somewhat dependent on the 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 which is usually -1) and set C on error. + +=over 4 =item B, B, B @@ -80,7 +130,20 @@ values. =item B, B -These correspond to fopen()/fdopen() arguments are the same. +These correspond to fopen()/fdopen() and the arguments are the same. +Return C and set C 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 may +not be set when C is returned if this limnit is exceeded. + +=item B + +While this currently exists in all three implementations perl itself +does not use it. I + +Perl prefers to C 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, B @@ -95,10 +158,16 @@ so it is (currently) legal to use C in perl sources. These correspond to fread() and fwrite(). Note that arguments are different, there is only one "count" and order has -"file" first. +"file" first. Returns a byte count if successful (which may be zero), +returns negative value and sets C on error. +Depending on implementation C may be C if operation +was interrupted by a signal. =item B +Depending on implementation C may be C if operation +was interrupted by a signal. + =item B, B These correspond to fputs() and fputc(). @@ -108,56 +177,103 @@ Note that arguments have been revised to have "file" first. This corresponds to ungetc(). Note that arguments have been revised to have "file" first. +Arranges that next read operation will return the byte B. +Despite the implied "character" in the name only values in the +range 0..0xFF are defined. Returns the byte B on success or -1 (C) 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 This corresponds to getc(). +Despite the c in the name only byte range 0..0xFF is supported. +Returns the character read or -1 (C) on error. =item B 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 This corresponds to ferror(). +Returns a true/false indication of whether there has been an IO error on the handle. =item B This corresponds to fileno(), note that on some platforms, -the meaning of "fileno" may not match Unix. +the meaning of "fileno" may not match Unix. Returns -1 if the handle has no +open descriptor associated with it. =item B -This corresponds to clearerr(), i.e., clears 'eof' and 'error' -flags for the "stream". +This corresponds to clearerr(), i.e., clears 'error' and (usually) 'eof' +flags for the "stream". Does not return a value. =item B This corresponds to fflush(). +Sends any buffered write data to the underlying file. +If called with C this may flush all open streams (or core dump). +Calling on a handle open for read only, or on which last operation was a read of some kind +may lead to undefined behaviour. -=item B +=item B -This corresponds to ftell(). +This corresponds to fseek(). +Sends buffered write data to the underlying file, or discards any buffered +read data, then positions the file desciptor as specified by B and B (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 which is a perl Configure value which may not be same +as stdio's C. -=item B +=item B -This corresponds to fseek(). +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 which is a perl Configure +value which may not be same as stdio's C. =item B, B -These correspond to fgetpos() and fsetpos(). If platform does not -have the stdio calls then they are implemented in terms of PerlIO_tell() -and PerlIO_seek(). +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 -This corresponds to rewind(). Note may be redefined -in terms of PerlIO_seek() at some point. +This corresponds to rewind(). It is usually defined as being + + PerlIO_seek(f,(Off_t)0L, SEEK_SET); + PerlIO_clearerr(f); + =item B This corresponds to tmpfile(), i.e., returns an anonymous -PerlIO which will automatically be deleted when closed. +PerlIO or NULL on error. +The system will attempt to automatically delete the file when closed. +On Unix the file is usually C-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. +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 + +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 when "dumping"; it has nothing to do with $| auto-flush.) =back @@ -165,9 +281,19 @@ PerlIO which will automatically be deleted when closed. 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 if perlio is implemented on top of (say) sfio -then mechanisms must exist to create a FILE * which can be passed -to library code which is going to use stdio calls. +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 fisrt step is to add this line: + + #define PERLIO_NOT_STDIO 0 + +I 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 @@ -176,9 +302,13 @@ to library code which is going to use stdio calls. Used to get a PerlIO * from a FILE *. May need additional arguments, interface under review. +The flags argument was meant to be used for read vs write vs read/write +information. In hindsight it would have been better to make it a char *mode +as in fopen/freopen. + =item B -Given an PerlIO * return a 'native' FILE * suitable for +Given a PerlIO * return a 'native' FILE * suitable for passing to code expecting to be compiled and linked with ANSI C I. @@ -198,77 +328,157 @@ of FILE * is complete. It is removed from list of 'exported' FILE *s, and associated PerlIO * should revert to original behaviour. -=item B - -This corresponds to setlinebuf(). Use is deprecated pending -further discussion. (Perl core uses it I when "dumping"; -it has nothing to do with $| auto-flush.) - =back -In addition to user API above there is an "implementation" interface +=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. This section is really of interest to only those -concerned with detailed perl-core behaviour or implementing a -PerlIO mapping. +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 - -Implementation can return pointer to current position in the "buffer" and -a count of bytes available in the buffer. +=item B -=item B +Returns true if implementation has all the interfaces required to +allow perl's C to "bypass" normal IO mechanism. +This can vary from handle to handle. -Return pointer to next readable byte in buffer. + PerlIO_fast_gets(f) = PerlIO_has_cntptr(f) && \ + PerlIO_canset_cnt(f) && \ + `Can set pointer into buffer' -=item B -Return count of readable bytes in the buffer. +=item B -=item B +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. -Implementation can adjust its idea of number of -bytes in the buffer. +=item B -=item B +Return count of readable bytes in the buffer. Zero or negative return means +no more bytes available. -Implementation has all the interfaces required to -allow perl's fast code to handle mechanism. +=item B - PerlIO_fast_gets(f) = PerlIO_has_cntptr(f) && \ - PerlIO_canset_cnt(f) && \ - `Can set pointer into buffer' +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 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 and C. +to C and C. The two values I be consistent +with each other (implementation may only use one or the other or may require both). + +=item B + +Implementation can adjust its idea of number of bytes in the buffer. +Do not use this - use PerlIO_fast_gets. =item B Obscure - set count of bytes in the buffer. Deprecated. -Currently used in only doio.c to force count < -1 to -1. +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 -Implementation has a buffer, and can return pointer +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 -Return I of buffer. +Return I of buffer. Access only positive offsets in the buffer +up to the value returned by PerlIO_get_bufsiz(). =item B -Return I of buffer. +Return the I 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 +(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. Use PerlIO_binmode() below for the portable +case. + +=item PerlIO_binmode(f,ptype,imode,layers) + +The hook used by perl's C operator. +B is perl's charcter for the kind of IO: + +=over 8 + +=item 'E' read + +=item 'E' write + +=item '+' read/write + +=back + +B is C or C. + +B is a string of layers to apply, only ":raw" or :"crlf" make +sense in the non USE_PERLIO case. + +Portable cases are: + + PerlIO_binmode(f,ptype,O_BINARY,":raw"); +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: + PERLIO_DEBUG=/dev/tty ./perl somescript some args + + Csh: + setenv 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