EMA C++ Configuration Guide : 4 Enterprise Message API Configuration Processing : 4.4 Configuring the Enterprise Message API Using Function Calls
 
4.4 Configuring the Enterprise Message API Using Function Calls
From an application standpoint, instantiating OmmConsumerConfig and OmmNiProviderConfig objects creates the initial configuration from the DefaultXML.h and the Enterprise Message API’s XML configuration file (if one exists). Certain variables can then be altered via function calls on the OmmConsumerConfig and OmmProviderConfig objects.
 
NOTE: Function calls override any settings in a configuration XML file.