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/***
*fseek.c - reposition file pointer on a stream** Copyright (c) 1985-2001, Microsoft Corporation. All rights reserved.**Purpose:* defines fseek() - move the file pointer to new place in file**Revision History:* 10-13-83 RN initial version* 06-26-85 TC added code to allow variable buffer lengths* 02-10-87 BCM fixed '%' mistakenly used for '/'* 03-04-87 JCR added errno settings* 04-16-87 JCR added _IOUNGETC support for bug fix and changes whence* from unsigned int to int (ANSI conformance)* 04-17-87 JCR fseek() now clears end-of-file indicator flag _IOEOF* (for ANSI conformance)* 04-21-87 JCR be smart about lseek'ing to the end of the file and* back* 09-17-87 SKS handle case of '\n' at beginning of buffer (FCRLF flag)* 09-24-87 JCR fixed an incorrect access to flag _IOEOF* 09-28-87 JCR Corrected _iob2 indexing (now uses _iob_index() macro).* 09-30-87 JCR Fixed buffer allocation bug, now use _getbuf()* 11-04-87 JCR Multi-thread support* 12-11-87 JCR Added "_LOAD_DS" to declaration* 01-13-88 JCR Removed unnecessary calls to mthread fileno/feof/ferror* 03-04-88 JCR Return value from read() must be treated as unsigned* value* 05-27-88 PHG Merged DLL and normal versions* 06-06-88 JCR Optimized _iob2[] references* 06-15-88 JCR Near reference to _iob[] entries; improve REG variables* 08-25-88 GJF Don't use FP_OFF() macro for the 386* 12-02-88 JCR Added _IOCTRLZ support (fixes bug pertaining to ^Z at* eof)* 04-12-89 JCR Ripped out all of the special read-only code. See the* comments in the routine header for more information.* 08-17-89 GJF Clean up, now specific to OS/2 2.0 (i.e., 386 flat* model). Also fixed copyright and indents.* 02-15-90 GJF Fixed copyright* 03-19-90 GJF Made calling type _CALLTYPE1, added #include* <cruntime.h> and removed #include <register.h>.* 05-29-90 SBM Use _flush, not [_]fflush[_lk]* 07-23-90 SBM Replaced <assertm.h> by <assert.h>* 10-02-90 GJF New-style function declarators.* 01-21-91 GJF ANSI naming.* 03-27-92 DJM POSIX support.* 08-08-92 GJF Use seek method constants!* 08-26-92 GJF Include unistd.h for POSIX build.* 04-06-93 SKS Replace _CRTAPI* with __cdecl* 05-24-93 GJF If the stream was opened for read-access-only, reduce* _bufsiz after flushing the stream. This should reduce* the expense of the next _filbuf call, and the overall* burden of seek-and-do-small-reads patterns of file* input.* 06-22-93 GJF Check _flag for _IOSETVBUF (new) before changing* buffer size.* 11-05-93 GJF Merged with NT SDK version. Also, replaced MTHREAD* with _MT.* 02-06-94 CFW assert -> _ASSERTE.* 02-20-95 GJF Merged in Mac version.* 03-07-95 GJF _[un]lock_str macros now take FILE * arg.* 03-02-98 GJF Exception-safe locking.* 05-17-99 PML Remove all Macintosh support.********************************************************************************/
#include <cruntime.h>
#include <stdio.h>
#include <file2.h>
#include <dbgint.h>
#ifdef _POSIX_
#include <unistd.h>
#else
#include <msdos.h>
#endif
#include <errno.h>
#include <malloc.h>
#include <io.h>
#include <stddef.h>
#include <internal.h>
#ifndef _POSIX_
#include <mtdll.h>
#endif
/***
*int fseek(stream, offset, whence) - reposition file pointer**Purpose:** Reposition file pointer to the desired location. The new location* is calculated as follows:* { whence=0, beginning of file }* <offset> bytes + { whence=1, current position }* { whence=2, end of file }** Be careful to coordinate with buffering.** - - - - - - - - - - - - -** [NOTE: We used to bend over backwards to try and preserve the current* buffer and maintain disk block alignment. This ended up making our* code big and slow and complicated, and slowed us down quite a bit.* Some of the things pertinent to the old implimentation:** (1) Read-only: We only did the special code path if the file was* opened read-only (_IOREAD). If the file was writable, we didn't* try to optimize.** (2) Buffering: We'd assign a buffer, if necessary, since the* later code might need it (i.e., call _getbuf).** (3) Ungetc: Fseek had to be careful NOT to save the buffer if* an ungetc had ever been done on the buffer (flag _IOUNGETC).** (4) Control ^Z: Fseek had to deal with ^Z after reading a* new buffer's worth of data (flag _IOCTRLZ).** (5) Seek-to-end-and-back: To determine if the new seek was within* the current buffer, we had to 'normalize' the desired location.* This means that we sometimes had to seek to the end of the file* and back to determine what the 0-relative offset was. Two extra* lseek() calls hurt performance.** (6) CR/LF accounting - When trying to seek within a buffer that* is in text mode, we had to go account for CR/LF expansion. This* required us to look at every character up to the new offset and* see if it was '\n' or not. In addition, we had to check the* FCRLF flag to see if the new buffer started with '\n'.** Again, all of these notes are for the OLD implimentation just to* remind folks of some of the issues involving seeking within a buffer* and maintaining buffer alignment. As an aside, I think this may have* been a big win in the 'old days' on floppy-based systems but on newer* fast hard disks, the extra code/complexity overwhelmed any gain.** - - - - - - - - - - - - -**Entry:* FILE *stream - file to reposition file pointer on* long offset - offset to seek to* int whence - origin offset is measured from (0=beg, 1=current pos,* 2=end)**Exit:* returns 0 if succeeds* returns -1 and sets errno if fails* fields of FILE struct will be changed**Exceptions:********************************************************************************/
#ifdef _MT /* multi-thread; define both fseek() and _lk_fseek() */
int __cdecl fseek ( FILE *stream, long offset, int whence ){ int retval;
_ASSERTE(stream != NULL);
_lock_str(stream);
__try { retval = _fseek_lk (stream, offset, whence); } __finally { _unlock_str(stream); }
return(retval);}
/***
*_fseek_lk() - Core fseek() routine (stream is locked)**Purpose:* Core fseek() routine; assumes that caller has the stream locked.** [See fseek() for more info.]**Entry: [See fseek()]**Exit: [See fseek()]**Exceptions:********************************************************************************/
int __cdecl _fseek_lk (
#else /* non multi-thread; just define fseek() */
int __cdecl fseek (
#endif /* rejoin common code */
FILE *str, long offset, int whence ){
REG1 FILE *stream;
_ASSERTE(str != NULL);
/* Init stream pointer */ stream = str;
if ( !inuse(stream) || ((whence != SEEK_SET) && (whence != SEEK_CUR) && (whence != SEEK_END)) ) { errno=EINVAL; return(-1); }
/* Clear EOF flag */
stream->_flag &= ~_IOEOF;
/* If seeking relative to current location, then convert to
a seek relative to beginning of file. This accounts for buffering, etc. by letting fseek() tell us where we are. */
if (whence == SEEK_CUR) { offset += _ftell_lk(stream); whence = SEEK_SET; }
/* Flush buffer as necessary */
#ifdef _POSIX_
/*
* If the stream was last read, we throw away the buffer so * that a possible subsequent write will encounter a clean * buffer. (The Win32 version of fflush() throws away the * buffer if it's read.) Write buffers must be flushed. */ if ((stream->_flag & (_IOREAD | _IOWRT)) == _IOREAD) { stream->_ptr = stream->_base; stream->_cnt = 0; } else { _flush(stream); }#else
_flush(stream);#endif
/* If file opened for read/write, clear flags since we don't know
what the user is going to do next. If the file was opened for read access only, decrease _bufsiz so that the next _filbuf won't cost quite so much */
if (stream->_flag & _IORW) stream->_flag &= ~(_IOWRT|_IOREAD); else if ( (stream->_flag & _IOREAD) && (stream->_flag & _IOMYBUF) && !(stream->_flag & _IOSETVBUF) ) stream->_bufsiz = _SMALL_BUFSIZ;
/* Seek to the desired locale and return. */
#ifdef _POSIX_
return(lseek(fileno(stream), offset, whence) == -1L ? -1 : 0);#else
return(_lseek(_fileno(stream), offset, whence) == -1L ? -1 : 0);#endif
}
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