This is about the new MongoDB C++ Driver (not the legacy one). I can insert a document this way:
value Value = document{}
<<"Key" <<"Value"
<<finalize;
cxxClient["db"]["collection"].insert_one(Value.view());
The above code insert a document with 1 field 'Key' of value 'Value'. I can insert string, int, float,... but just can't figure out how to insert ISODate. The new MongoDB C++ Driver should come with more examples in documentation.