Why does the program output 01 instead of 00?

#include <iostream> namespace A { extern "C" int x = 0; }; namespace B { extern "C" int x; }; int main() { std::cout << B::x; A::x = 1; std::cout << B::x; }
  • And why should she output 00 ? Where is the rationale for the expected behavior? Without it, your question sounds like "why in the program 2 + 2 is 4, not 5". - AnT

2 answers 2

The program displays 01 because it should output 01 . Language specification clearly speaks

If you’re referring to the namespace scopes, you’ll refer to the same variable.

Two variable declarations with C-linking with the same name (ignoring the qualifying namespace names), which are located in different namespaces, refer to the same variable.

Both declarations - A::x and B::x - declare the same variable.

The question itself is somewhat surprising. Under what circumstances can this be expected from such an output program 00 ? If A::x and B::x declare different variables? But then the program would not compile at all due to the lack of definition for B::x .

    extern "C" spoils everything :) - in fact, you declare a single variable x in two namespaces, which, being extern "C" , knows nothing about namespaces ...

    Try to define the second variable - well, type

     namespace B { extern "C" int x = 3; };

    and you will receive the appropriate messages when compiling.