ungetc.c

来自「Algorithms for Image Processing and Comp」· C语言 代码 · 共 33 行

/* This is file UNGETC.C */
/* This file may have been modified by DJ Delorie (Jan 1991).  If so,
** these modifications are Coyright (C) 1993 DJ Delorie, 24 Kirsten Ave,
** Rochester NH, 03867-2954, USA.
*/

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)ungetc.c	5.3 (Berkeley) 3/26/86";
#endif LIBC_SCCS and not lint

#include <stdio.h>

int
ungetc(c, iop)
     int c;
     register FILE *iop;
{
	if (c == EOF || (iop->_flag & (_IOREAD|_IORW)) == 0 ||
	    iop->_ptr == NULL || iop->_base == NULL)
		return (EOF);

	if (iop->_ptr == iop->_base)
		if (iop->_cnt == 0)
			iop->_ptr++;
		else
			return (EOF);

	iop->_cnt++;
	*--iop->_ptr = c;

	return (c);
}