Function overload with C++ using VS2017

Question

I'm having a problem compiling this simple code in VS2017, but the code is working fine in Code Blocks. In VS2017 I've got this error message:

C2382 'abs':redefinition; different exception specifications

Here is the code below:

#include <iostream>
using namespace std;

int abs(int i);
float abs(float f);

int main()
{
    cout << abs(-10) << endl;
    cout << abs(-11.0f) << endl;
    return 0;
}
int abs(int i)
{
    cout << "Using integer abs()\n";
    return i<0 ? -i : i;
}
float abs(float f)
{
    cout << "Using float abs()\n";
    return f<0.0f ? -f : f;
}

Why are you declaring a library function yourself instead of including the appropriate header? — StoryTeller - Unslander Monica, Feb 11 '18 at 21:24
There's an `abs` function in the standard library. `using namespace std` is causing the problem, but you shouldn't use the name `abs` in the global namespace anyway to avoid conflict with C — Justin, Feb 11 '18 at 21:24
See [`std::abs`](http://en.cppreference.com/w/cpp/numeric/math/fabs). — Some programmer dude, Feb 11 '18 at 21:25
Also see [Why is “using namespace std” considered bad practice?](https://stackoverflow.com/questions/1452721/why-is-using-namespace-std-considered-bad-practice) — Some programmer dude, Feb 11 '18 at 21:25

Arnav Borborah · Accepted Answer · 2018-02-11T21:34:55.330

The reason you are getting an error is because there are already a set of functions called abs in the standard library, which would normally have to be accessed with std::, but using namespace std removes that qualifier, creating a name collision between all the functions. Thus, you should either change the name of your functions to something like myAbs, or remove the using namespace std. An even better change would be to both remove the using statement and rename the function.

Your code exhibits a key reason to why using namespace std should be avoided, since it can cause namespace collisions and unnecessary confusion.

Function overload with C++ using VS2017

1 Answers1