Question

I made a header file sampleheader.h with following code:

namespace sample_namespace
{
    int add(int n1,int n2)
    {
        return (n1 + n2);
    }
}

Now my main.cpp file is:

#include <iostream>
#include "sampleheader.h"
using namespace std;

int add(int n1, int n2)
{
  return (n1 + n2);
}

int main(void)
{
    using namespace sample_namespace;
    //cout<<add(5,7);
}

The project is built with no warning if i leave that line commented.It is understandable because the local add() function is defined in the global scope and add() function is made visible in the scope of main(). So no name conflict happens.

However, if I remove the comments, I get the following error:

"Ambiguous call to overloaded function"

First of all there should be no name conflict at all as explained by me above (if I’m right). But, if at all there is a name conflict why is it that it is notified by compiler only when I call the function. Such type of error should be shown as soon as a name conflicts (if at all).

Any help is appreciated.

Answer 1

“using namespace” does not hide other implementations. What it does in this case is make it ambiguous.

You have both sample_namespace::add and ::add with the same signature. Since you don’t explicitly say which one to use, the compiler can’t tell.

Declaring both functions is legal and unambiguous (which is why the compiler only complains when you use the function).