Why is my log in the std namespace?

Question

In the code below, I define a trivial log function. In main I try not to call it; I call std::log. Nevertheless, my own

Answer 1

Because you've overridden it in the global namespace. Using a namespace avoids that danger if you don't want to move on to a safer, cleaner language like Nim for example.

Proper use of namespace demo:

#include 
#include   // Uses ::log, which would be the log() here if it were not in a namespace, see http://stackoverflow.com/questions/11892976/why-is-my-log-in-the-std-namespace

// Silently overrides std::log
//double log(double d) { return 420; }

namespace uniquename {
    using namespace std;  // So we don't have to waste space on std:: when not needed.

    double log(double d) {
        return 42;
    }

    int main() {
        cout << "Our log: " << log(4.2) << endl;
        cout << "Standard log: " << std::log(4.2);
        return 0;
    }
}

// Global wrapper for our contained code.
int main() {
    return uniquename::main();
}

Output:

Our log: 42
Standard log: 1.43508