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#include <iostream>
 
namespace a{}
namespace b{}
 
void a::foo()
{
    std::cout << "a foo" << std::endl;
}
 
void b::foo()
{
    std::cout << "b foo" << std::endl;
}
 
int main()
{
    a::foo();
    b::foo();
}

prog.cpp:6:13: error: ‘void a::foo()’ should have been declared inside ‘a’
prog.cpp:11:13: error: ‘void b::foo()’ should have been declared inside ‘b’
prog.cpp: In function ‘void b::foo()’:
prog.cpp:11:13: error: ‘void b::foo()’ conflicts with a previous declaration
prog.cpp:6:6: note: previous declaration ‘void a::foo()’
prog.cpp: In function ‘int main()’:
prog.cpp:18:5: error: ‘foo’ is not a member of ‘a’
prog.cpp:18:5: note: suggested alternative:
prog.cpp:6:6: note:   ‘a::foo’
prog.cpp:19:5: error: ‘foo’ is not a member of ‘b’
prog.cpp:19:5: note: suggested alternative:
prog.cpp:6:6: note:   ‘a::foo’

Standard output is empty