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Tricks of the Windows Gam…ming Gurus (2nd Edition)
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Disc2.iso
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vc98
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crt
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src
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ungetc.c
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C/C++ Source or Header
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1998-06-17
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4KB
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145 lines
/***
*ungetc.c - unget a character from a stream
*
* Copyright (c) 1985-1997, Microsoft Corporation. All rights reserved.
*
*Purpose:
* defines ungetc() - pushes a character back onto an input stream
*
*******************************************************************************/
#include <cruntime.h>
#include <stdio.h>
#include <file2.h>
#include <dbgint.h>
#include <internal.h>
#include <mtdll.h>
#ifdef _MT
/***
*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 __cdecl ungetc (
REG2 int ch,
REG1 FILE *stream
)
{
int retval;
_ASSERTE(stream != NULL);
_lock_str(stream);
retval = _ungetc_lk (ch, stream);
_unlock_str(stream);
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 __cdecl _ungetc_lk (
REG2 int ch,
FILE *str
)
{
#else /* _MT */
int __cdecl ungetc (
REG2 int ch,
FILE *str
)
{
#endif /* _MT */
REG1 FILE *stream;
_ASSERTE(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);
}