Question

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What is the meaning of prepended double colon “::” to class name?

I have been looking at a legacy C++ code and it had something like this:

::putenv(local_tz_char);
::tzset();

What does this syntax of prepending “::” to the function calls mean? Google-fu is failing me.

Answer 1

It means that the functions putenv() and tzset() will be looked up by the compiler in the global namespace.

Example

#include <iostream>

using namespace std;

//global function
void foo()
{
    cout << "This function will be called by bar()";
}

namespace lorem
{
    void foo()
    {
        cout << "This function will not be called by bar()";
    }

    void bar()
    {
        ::foo();
    }
}

int main()
{
    lorem::bar(); //will print "This function will be called by bar()"
    return 0;
}