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CPM OPERATING SYSTEMS/CPM 68K/1.0X SOURCES/v102a/clib/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
+*	      -------------------------------------------------
+*	Copyright 1982 by Digital Research Inc.  All rights reserved.
+*
+*	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	<portab.h>			/* Include std definitions  */
+#include	<cpm.h>				/* and CP/M definitions	    */
+#include	<errno.h>
+FD	 *_chkc(ch)				/****************************/
+REG	UWORD	 ch;				/* Facilitate error check   */
+{						/*			    */
+	REG	FD *xcb;			/* -> CCB		    */
+						/****************************/
+	if(ch >= MAXCCBS)			/* Is channel in range?	    */
+		RETERR(NULL,EBADF);		/* No, quit now.	    */
+						/*			    */
+	xcb = _getccb(ch);			/* xcb -> ccb for channel   */
+	if((xcb->flags & OPENED) == 0)		/* Is channel OPEN?	    */
+		RETERR(NULL,EBADF);		/* Noooooooo!!		    */
+	return(xcb);				/* Else, return pointer     */
+}						/****************************/