What's the difference between abs and fabs?

Question

I checked the difference between abs and fabs on python here

As I understand there are some difference regarding the speed and the passed t

Answer 1

With C++ 11, using abs() alone is very dangerous:

#include 
#include 

int main() {
    std::cout << abs(-2.5) << std::endl;
    return 0;
}

This program outputs 2 as a result. (See it live)

Always use std::abs():

#include 
#include 

int main() {
    std::cout << std::abs(-2.5) << std::endl;
    return 0;
}

This program outputs 2.5.

You can avoid the unexpected result with using namespace std; but I would adwise against it, because it is considered bad practice in general, and because you have to search for the using directive to know if abs() means the int overload or the double overload.