Have a gmock method, and during test, need to set the out parameter to variable address. So that the out parameter of dequeue, which is data points to variable ch; MOCK_METHOD1(dequeue, void(void* data)); char ch = 'm'; void* a = (void*)&ch; EXPECT_CALL(FQO, dequeue(_)) .WillOnce(/*here I need to set argument to a*/); I tried to figure out side effects: https://code.google.com/p/googlemock/wiki/V1_7_CheatSheet#Side_Effects but keep getting an error.