REQUEST_CHOICE(3G)

NAME

request_choice − wait for a measure to be triggered, then return the measured value.

SYNOPSIS

C SYNTAX

void request_choice(fildes,ordinal,timeout,valid,value);
int fildes,ordinal,*valid,*value;
float timeout;

FORTRAN77 SYNTAX

        subroutine request_choice(fildes,ordinal,timeout,
        valid,value)
        integer*4 fildes,ordinal,valid,value
        real timeout

PASCAL SYNTAX

procedure request_choice(fildes,ordinal:integer;
timeout:real;var valid,value:integer);

HP-UX COMPATIBILITY

Level: HP-UX/STANDARD

Origin: ANSI Computer Graphics Interface

DESCRIPTION

INPUT PARAMETERS

fildes
is an integer file descriptor returned by gopen when an I/O path to a graphics device is opened.
ordinal
is a logical device number ranging from 1 to number of devices of this class.
timeout
is the time, in seconds, to wait for a trigger.

OUTPUT PARAMETERS

valid
is set to FALSE (0 in Pascal) if data is invalid, If set to FALSE, then *value is undefined.

If set to TRUE (1 in Pascal) if data is valid.
value
is set to the current measure value if valid is set to TRUE (1 in Pascal)

DISCUSSION

Request_choice returns the measure value of the device specified by fildes and ordinal when a trigger occurs, when the user indicates a ’break’ action, or when the time period specified by timeout is exceeded. If the request was not previously posted with initiate_request and no request data is ready for this device, it is posted by this call. If a request was previously posted but not yet satisfied, the timeout runs from the time this call was made. Valid is set to FALSE if a break occurs, if the timeout period is exceeded, or if the device is not initialized.

A request may be performed on an input device while it is enabled for event generation. The mode of (events enabled/events disabled) is saved by the device and restored after the request has been satisfied. The request data does not go into the event queue, but into a separate virtual register.

Whether a previously posted request is ready can be read with inquire_request_status.

A previously posted and satisfied but not read request can be discarded by issuing a request_choice with a zero timeout and discarding the result.

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