180 lines
5.3 KiB
C
180 lines
5.3 KiB
C
/***
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*ungetc.c - unget a character from a stream
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*
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* Copyright (c) 1985-2001, Microsoft Corporation. All rights reserved.
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*
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*Purpose:
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* defines ungetc() - pushes a character back onto an input stream
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*
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*Revision History:
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* 09-02-83 RN initial version
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* 04-16-87 JCR added support for _IOUNGETC flag
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* 08-04-87 JCR (1) Added _IOSTRG check before setting _IOUNGETC flag.
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* (2) Allow an ugnetc() before a read has occurred (get a
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* buffer (ANSI). [MSC only]
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* 09-28-87 JCR Corrected _iob2 indexing (now uses _iob_index() macro).
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* 11-04-87 JCR Multi-thread support
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* 12-11-87 JCR Added "_LOAD_DS" to declaration
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* 05-25-88 JCR Allow an ungetc() before read for file opened "r+".
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* 05-31-88 PHG Merged DLL and normal versions
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* 06-06-88 JCR Optimized _iob2 references
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* 06-15-88 JCR Near reference to _iob[] entries; improve REG variables
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* 08-25-88 GJF Don't use FP_OFF() macro for the 386
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* 04-11-89 JCR Removed _IOUNGETC flag, fseek() no longer needs it
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* 08-17-89 GJF Clean up, now specific to OS/2 2.0 (i.e., 386 flat
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* model). Also fixed copyright and indents.
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* 02-16-90 GJF Fixed copyright
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* 03-20-90 GJF Made calling type _CALLTYPE1, added #include
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* <cruntime.h> and removed #include <register.h>.
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* 07-23-90 SBM Replaced <assertm.h> by <assert.h>
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* 08-13-90 SBM Compiles cleanly with -W3
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* 10-03-90 GJF New-style function declarators.
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* 11-07-92 SRW Dont modify buffer if stream opened by sscanf
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* 04-06-93 SKS Replace _CRTAPI* with __cdecl
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* 04-26-93 CFW Wide char enable.
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* 04-30-93 CFW Remove wide char support to ungetwc.c.
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* 09-06-94 CFW Replace MTHREAD with _MT.
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* 02-06-94 CFW assert -> _ASSERTE.
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* 03-07-95 GJF _[un]lock_str macros now take FILE * arg.
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* 03-02-98 GJF Exception-safe locking.
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*
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*******************************************************************************/
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#include <cruntime.h>
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#include <stdio.h>
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#include <file2.h>
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#include <dbgint.h>
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#include <internal.h>
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#include <mtdll.h>
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#ifdef _MT /* multi-thread; define both ungetc and _lk_ungetc */
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/***
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*int ungetc(ch, stream) - put a character back onto a stream
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*
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*Purpose:
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* Guaranteed one char pushback on a stream as long as open for reading.
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* More than one char pushback in a row is not guaranteed, and will fail
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* if it follows an ungetc which pushed the first char in buffer. Failure
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* causes return of EOF.
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*
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*Entry:
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* char ch - character to push back
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* FILE *stream - stream to push character onto
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*
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*Exit:
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* returns ch
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* returns EOF if tried to push EOF, stream not opened for reading or
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* or if we have already ungetc'd back to beginning of buffer.
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*
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*Exceptions:
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*
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*******************************************************************************/
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int __cdecl ungetc (
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REG2 int ch,
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REG1 FILE *stream
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)
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{
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int retval;
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_ASSERTE(stream != NULL);
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_lock_str(stream);
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__try {
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retval = _ungetc_lk (ch, stream);
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}
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__finally {
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_unlock_str(stream);
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}
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return(retval);
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}
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/***
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*_ungetc_lk() - Ungetc() core routine (locked version)
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*
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*Purpose:
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* Core ungetc() routine; assumes stream is already locked.
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*
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* [See ungetc() above for more info.]
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*
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*Entry: [See ungetc()]
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*
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*Exit: [See ungetc()]
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*
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*Exceptions:
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*
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*******************************************************************************/
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int __cdecl _ungetc_lk (
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REG2 int ch,
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FILE *str
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)
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{
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#else /* non multi-thread; just define ungetc */
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int __cdecl ungetc (
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REG2 int ch,
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FILE *str
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)
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{
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#endif /* rejoin common code */
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REG1 FILE *stream;
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_ASSERTE(str != NULL);
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/* Init stream pointer and file descriptor */
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stream = str;
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/* Stream must be open for read and can NOT be currently in write mode.
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Also, ungetc() character cannot be EOF. */
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if (
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(ch == EOF) ||
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!(
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(stream->_flag & _IOREAD) ||
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((stream->_flag & _IORW) && !(stream->_flag & _IOWRT))
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)
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)
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return(EOF);
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/* If stream is unbuffered, get one. */
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if (stream->_base == NULL)
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_getbuf(stream);
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/* now we know _base != NULL; since file must be buffered */
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if (stream->_ptr == stream->_base) {
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if (stream->_cnt)
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/* my back is against the wall; i've already done
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* ungetc, and there's no room for this one
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*/
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return(EOF);
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stream->_ptr++;
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}
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if (stream->_flag & _IOSTRG) {
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/* If stream opened by sscanf do not modify buffer */
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if (*--stream->_ptr != (char)ch) {
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++stream->_ptr;
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return(EOF);
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}
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} else
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*--stream->_ptr = (char)ch;
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stream->_cnt++;
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stream->_flag &= ~_IOEOF;
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stream->_flag |= _IOREAD; /* may already be set */
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return(0xff & ch);
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}
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