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/***
*ungetc.c - unget a character from a stream
*
* Copyright (c) 1985-1993, Microsoft Corporation. All rights reserved.
*
*Purpose:
* defines ungetc() - pushes a character back onto an input stream
*
*Revision History:
* 09-02-83 RN initial version
* 04-16-87 JCR added support for _IOUNGETC flag
* 08-04-87 JCR (1) Added _IOSTRG check before setting _IOUNGETC flag.
* (2) Allow an ugnetc() before a read has occurred (get a
* buffer (ANSI). [MSC only]
* 09-28-87 JCR Corrected _iob2 indexing (now uses _iob_index() macro).
* 11-04-87 JCR Multi-thread support
* 12-11-87 JCR Added "_LOAD_DS" to declaration
* 05-25-88 JCR Allow an ungetc() before read for file opened "r+".
* 05-31-88 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
* 04-11-89 JCR Removed _IOUNGETC flag, fseek() no longer needs it
* 08-17-89 GJF Clean up, now specific to OS/2 2.0 (i.e., 386 flat
* model). Also fixed copyright and indents.
* 02-16-90 GJF Fixed copyright
* 03-20-90 GJF Made calling type _CALLTYPE1, added #include
* <cruntime.h> and removed #include <register.h>.
* 07-23-90 SBM Replaced <assertm.h> by <assert.h>
* 08-13-90 SBM Compiles cleanly with -W3
* 10-03-90 GJF New-style function declarators.
* 11-07-92 SRW Dont modify buffer if stream opened by sscanf
* 04-26-93 CFW Wide char enable.
* 04-30-93 CFW Remove wide char support to ungetwc.c.
*
*******************************************************************************/
#include <cruntime.h>
#include <stdio.h>
#include <file2.h>
#include <assert.h>
#include <internal.h>
#include <os2dll.h>
#ifdef MTHREAD /* multi-thread; define both ungetc and _lk_ungetc */
/***
*int ungetc(ch, stream) - put a character back onto a stream
*
*Purpose:
* Guaranteed one char pushback on a stream as long as open for reading.
* More than one char pushback in a row is not guaranteed, and will fail
* if it follows an ungetc which pushed the first char in buffer. Failure
* causes return of EOF.
*
*Entry:
* char ch - character to push back
* FILE *stream - stream to push character onto
*
*Exit:
* returns ch
* returns EOF if tried to push EOF, stream not opened for reading or
* or if we have already ungetc'd back to beginning of buffer.
*
*Exceptions:
*
*******************************************************************************/
int _CRTAPI1 ungetc (
REG2 int ch,
REG1 FILE *stream
)
{
int retval;
int index;
assert(stream != NULL);
index = _iob_index(stream);
_lock_str(index);
retval = _ungetc_lk (ch, stream);
_unlock_str(index);
return(retval);
}
/***
*_ungetc_lk() - Ungetc() core routine (locked version)
*
*Purpose:
* Core ungetc() routine; assumes stream is already locked.
*
* [See ungetc() above for more info.]
*
*Entry: [See ungetc()]
*
*Exit: [See ungetc()]
*
*Exceptions:
*
*******************************************************************************/
int _CRTAPI1 _ungetc_lk (
REG2 int ch,
FILE *str
)
{
#else /* non multi-thread; just define ungetc */
int _CRTAPI1 ungetc (
REG2 int ch,
FILE *str
)
{
#endif /* rejoin common code */
REG1 FILE *stream;
assert(str != NULL);
/* Init stream pointer and file descriptor */
stream = str;
/* Stream must be open for read and can NOT be currently in write mode.
Also, ungetc() character cannot be EOF. */
if (
(ch == EOF) ||
!(
(stream->_flag & _IOREAD) ||
((stream->_flag & _IORW) && !(stream->_flag & _IOWRT))
)
)
return(EOF);
/* If stream is unbuffered, get one. */
if (stream->_base == NULL)
_getbuf(stream);
/* now we know _base != NULL; since file must be buffered */
if (stream->_ptr == stream->_base) {
if (stream->_cnt)
/* my back is against the wall; i've already done
* ungetc, and there's no room for this one
*/
return(EOF);
stream->_ptr++;
}
if (stream->_flag & _IOSTRG) {
/* If stream opened by sscanf do not modify buffer */
if (*--stream->_ptr != (char)ch) {
++stream->_ptr;
return(EOF);
}
} else
*--stream->_ptr = (char)ch;
stream->_cnt++;
stream->_flag &= ~_IOEOF;
stream->_flag |= _IOREAD; /* may already be set */
return(0xff & ch);
}
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