Anonymous namespace - has sense in both headers and code files?

Question

test.cpp

#include "test.hpp"

void f1() { }

namespace {
   void f2() {}
}

namespace test {
   void f3() { }
}

Please correct me if I'm wrong, but:

• f1 can be called from outside if it is declared in the header file or an extern statement is used
• f2 can't be called from outside
• f3 can be called from outside if it is declared in the header file (and properly prefixed - test::). If it is not declared in a header, it can't be called?

Am I right?

Answer 1

Your question title is misleading. Don't put an anonymous namespace in a header, ever.

f2 can't be called from outside of test.cpp, correct.

f1 and f3 can be called if appropriate declarations are available. These can be in a header, but nothing stops other .cpp files from simply having the code that would be in a header, even if you don't provide one.

Also, extern is not needed for function declarations.

void f1();
namespace test {
  void f3();
}