a function definition cannot appear inside another function, but a function declaration can. Inside the function bool clusterLabelling(), after bool inTback(const tIndex_t index), the only thing that can follow is the semicolon (which would make that line a function declaration).
Thanks vlad and cubbi, but vlad's solution looks a little strange to me yet. I am going to declare the function inside the function clusterLabeling() and define it after it. Because I need to use datas from clusterLabeling().
But it seems my idea don't work, compilation error message shows all the