Avoiding compiler issues with abs()

Question

When using the double variant of the std::abs() function without the std with g++ 4.6.1, no warning or error is given.

Answer 1

The function you are using is actually the integer version of abs, and GCC does an implicit conversion to integer.

This can be verified by a simple test program:

#include 
#include 

int main()
{
    double a = -5.4321;
    double b = std::abs(a);
    double c = abs(a);

    std::cout << "a = " << a << ", b = " << b << ", c = " << c << '\n';
}

Output is:

a = -5.4321, b = 5.4321, c = 5

To get a warning about this, use the -Wconversion flag to g++. Actually, the GCC documentation for that option explicitly mentions calling abs when the argument is a double. All warning options can be found here.