How to call a function within GLFW window ?

See more:

OpenGL

C++14

I have GLFW window, and I've defined a specific height and width for it. Here's my GLFW window :

GLFWwindow *window = glfwCreateWindow( WIDTH, HEIGHT, "Exercise 3" , nullptr, nullptr );

And I want to call FPS in my window title. Side by side with my own title, like "My Title.." | FPS.
I came across FPS counter function, here :

double calcFPS(double theTimeInterval = 1.0, string theWindowTitle = "NONE"){...

What I have tried:

I can't seem to call the function from my main loop where I create my GLFW window as well. When I call the function and replace the function input parameter (2nd parameter) using my own GLFW window, I get error "No matching function for call to..". Any suggestion ?