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CPM OPERATING SYSTEMS/CPM 68K/1.0X SOURCES/v101/klib/chkc.c

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+/*****************************************************************************
+*
+*	      C H A N N E L   N U M B E R   V A L I D A T I O N
+*	      -------------------------------------------------
+*
+*	This routine is used to validate a channel number and return the
+*	pointer to the ccb area.  The channel must be in range and open.
+*
+*	Calling Sequence:
+*
+*		ccbptr = _chkc(ch);
+*
+*	Where:
+*
+*		ch	Is the channel number
+*		ccbptr	Is the returned ccb address
+*
+*****************************************************************************/
+#include	"stdio.h"			/* Include std definitions  */
+#include	"cpm.h"				/* and CP/M definitions	    */
+FILE	 *_chkc(ch)				/****************************/
+	UWORD	 ch;				/* Facilitate error check   */
+{						/*			    */
+	REG	FILE *xcb;			/* -> CCB		    */
+	EXTERN	FILE *_getc();			/* converts fd to fp	    */
+						/****************************/
+	if(ch >= MAXFILE)			/* Is channel in range?	    */
+		return(FAILURE);		/* No, quit now.	    */
+						/*			    */
+	xcb = _getc(ch);			/* xcb -> ccb for channel   */
+	if((xcb->flags & OPENED) == 0)		/* Is channel OPEN?	    */
+		return (FAILURE);		/* Noooooooo!!		    */
+	return(xcb);				/* Else, return pointer     */
+}						/****************************/