c++ - What causes std::bad_function_call?

Question

I've seen a few questions that refer to the std::bad_function_call exception, but haven't been able to find out any by Googling about what causes this exception.

What kind of behavior is supposed to cause this exception? Can you give me minimal examples that don't have other semantic problems also going on?

question from:https://stackoverflow.com/questions/5567287/what-causes-stdbad-function-call

Answer 1

Sure- the easiest is where you try to call a std::function that's empty.

int main() {
    std::function<int()> intfunc;
    int x = intfunc(); // BAD
}