To use a function defined in another file with g++, you need to follow a few steps.First, make sure the function is declared in a header file (.h) that is included in both the file where the function is defined and the file where you want to use the function.Next, compile the file where the function is defined using g++. This will generate an object file (.o).Then, compile the file where you want to use the function, along with the object file generated in the previous step.