The Get sample programs

The Get sample programs get messages from a queue using the MQGET call.

See Features demonstrated in the sample programs on Multiplatforms for the names of these programs.

Design of the Get sample program

The program opens the target queue using the MQOPEN call with the MQOO_INPUT_AS_Q_DEF option. If it cannot open the queue, the program displays an error message containing the reason code returned by the MQOPEN call.

For each message on the queue, the program uses the MQGET call to remove the message from the queue, then displays the data contained in the message. The MQGET call uses the MQGMO_WAIT option, specifying a WaitInterval of 15 seconds, so that the program waits for this period if there is no message on the queue. If no message arrives before this interval expires, the call fails and returns the MQRC_NO_MSG_AVAILABLE reason code.

The program demonstrates how we must clear the MsgId and CorrelId fields of the MQMD structure after each MQGET call because the call sets these fields to the values contained in the message it retrieves. Clearing these fields means that successive MQGET calls retrieve messages in the order in which the messages are held in the queue.

The MQGET call specifies a buffer of fixed size. If a message is longer than this buffer, the call fails and the program stops.

The program continues until either the MQGET call returns the MQRC_NO_MSG_AVAILABLE reason code or the MQGET call fails. If the call fails, the program displays an error message that contains the reason code.

The program then closes the queue using the MQCLOSE call.

• Running the amqsget and amqsgetc samples
  

Parent topic: Use the sample programs on Multiplatforms