Specifying device usage using the DSUSE call

GDDM V3R2 Base Application Programming Guide

Specifying device usage using the DSUSE call

GDDM V3R2 Base Application Programming Guide
SC33-0867-01

In your application you can open several different devices, issuing a DSOPEN call for each one. Opening a device has, in itself, no effect on the program until GDDM is informed that the program needs to use a particular device.

DSUSE indicates which device should be used for future output. DSUSE also performs an implicit DSDROP (see "Discontinuing use of a device, using DSDROP" in topic 18.3). This is the format for DSUSE:


     CALL DSUSE(1,11);        /* Use device 11 as the primary device */

The first parameter states whether the device should be used as a primary device or an alternate device.
The primary device is usually a display screen; it is the main target device for the program's output. It is possible to request "snapshots" or copies of the primary device to be made. In that case, the copies are sent to an alternate device, usually a printer. The way in which these copies are made is addressed in "Copying graphics to a printer using call GSCOPY" in topic 20.6.3.
So, the first parameter is set to 1 if the device is to be used as a primary device. It is set to 2 to request usage as an alternate device.
The second parameter is the device identifier-the number assigned to the device when DSOPEN was issued.

At any one time you can have one current primary device and (optionally) one current alternate device.

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