IBM MQ 中的关联 ID 和消息 ID

Question

For a c++ and c program, I am trying to set a value for msgId or CorrelId for a particular message in IBM MQ, that will be later put to a topic. But there's an error of "Expression must be a modifiable L-value" for both the ids.

I defined the ids as

MQBYTE24 MsgId;
MQBYTE24 CorrelId;

and the MQMD is defined as default:

MQMD md = {MQMD_DEFAULT};

I cannot use the #define directive as I am trying to single out a message to be put to a topic from the publisher's end. Receive all the messages for subscriber and check for the particular message.

Is my approach of using correlIds or MsgIds correct or is there a better way for doing this?

Answer 1

I would expect you to have some code that looks like the following:-

memcpy(md.CorrelId, CorrelId, MQ_MSG_ID_LENGTH);

Please also remember that the message ID that you MQPUT to a topic does not end up at the subscribers. A new message ID is created for each copy of the published message that is given to each subscriber. You should use the Correlation ID instead to have it flow through to the subscriber, and ensure the subscribers are made correctly to receive the publishers correlation ID.

Read IBM MQ Little Gem #31: Publisher's CorrelId for more information about this.