OnixS C++ FIX Engine  3.25.0
API Documentation
Using QuickFIX Dictionaries

FIX Engine supports dictionaries in the QuickFIX xml format, so you can use it as it is. However, there are some details:

EngineSettings settings;
settings.dictionaryFile("QuickFixDictionary.xml");
Engine::init(settings);
Dictionary quickFixDictionary("QuickFixDictionary");
Session sessionWithQuickFixDictionary("Sender", "Target", quickFixDictionary, &defaultListener);