Why would you write :: with no preceding namespace? (e.g. ::atof)

If you go to the accepted answer of this post

Could someone please elaborate on why he uses:

double temp = ::atof(num.c_str());

and not simply

double temp = atof(num.c_str());

Also, is it considered a good practice to use that syntax when you use "pure" global functions?

It says use the global version, not one declared in local scope. So if someone's declared an atof in your class, this'll be sure to use the global one.

Have a look at Wikipedia on this subject:

#include <iostream>

using namespace std;

int n = 12;   // A global variable

int main() {
    int n = 13;   // A local variable
    cout  << ::n << endl;  // Print the global variable: 12
    cout  << n   << endl;  // Print the local variable: 13
}