We are writing C++ code which needs messaging. Is there a free/open-source and stable AMQP server available that has equally stable C++ client library with it. We also need
AMQP can be quite complex to understand -- I suggest Using Protocol Buffers to code your communication layer, it generates both python and C++. if your needs are too complicated I would suggest ICE as it supports every programming language you can think of, and I believe it also handles the protocol buffers format.
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If you are going to use AMQP, you should look at Zero MQ. It has a C++ implementation of AMQP. However they are porting it to a pure-C implementation.