c++ - Invalid use of qualified name -

i'm trying following:

#include <iostream>  namespace {     extern int j; }  int main() {     int a::j=5;     std::cout << a::j; }

but i've error: invalid use of qualified-name ‘a::j’. please explain why error occurred?

please explain why error occurred?

the language doesn't allow define namespace-scope variables inside functions. definition has either in namespace a:

namespace {     int j = 5; }

or in surrounding (global) namespace:

int a::j = 5;

you can, of course, assign value variable inside function:

int main() {     a::j = 5;     // ... }

but you'll need definition somewhere, since program doesn't have one.

Brent