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CPM OPERATING SYSTEMS/CPM 68K/1.0X SOURCES/v101/clib/ungetc.c

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+/**************************************************************************
+*
+*			u n g e t c   F u n c t i o n
+*			-----------------------------
+*	Copyright 1982 by Digital Research Inc.  All rights reserved.
+*
+*	"ungetc" puts a char back into its (read only) stream.  It's
+*	guaranteed to work for at least one char, provided the
+*	stream is buffered and something has been read.
+*
+*	Calling sequence:
+*		ret = ungetc(c,stream)
+*	Where:
+*		ret = c if it worked, FAILURE o.w.
+*		c   = char to push back
+*		stream -> (FILE *) place to push back to
+*
+*****************************************************************************/
+#include <stdio.h>
+WORD ungetc(c,sp)				/****************************/
+REG	WORD c;					/* char to unget	    */
+REG	FILE *sp;				/* stream to unget to	    */
+{						/****************************/
+	if( c == EOF )				/* no allowed if EOF	    */
+		return(FAILURE);		/*			    */
+	if( sp->_flag & _IOREAD			/* if file is read able	    */
+	    && sp->_base != NULL  		/*   and something's read   */
+	    && sp->_ptr > sp->_base )		/*   and buffer not empty   */
+	{					/* then...		    */
+		*--sp->_ptr = c;		/* back up buffer & store   */
+		sp->_cnt++;			/* there's one more byte    */
+		return(c);			/* it worked!		    */
+	}					/****************************/
+	return(FAILURE);			/* it didn't work...	    */
+}						/****************************/