CODEWITHSUNDEEP
c++staticinner-classesclass-variablesqualified-name
Nick Haman
Nick Haman

Reputation: 11

Undefined Reference in C++ using static class

I've been looking for an answer to this for several hours. Even though I have a workaround I'd like to understand the problem. I get an undefined reference error when linking the following:

.h:

class Test
{
public:
    class Class1
    {
    public:
        Class1(int i);
        int x;      
        void Inc();
    };
    
    static Class1 one;  
    static int F1();    
    
    
};

.cpp:

#include "Test.h"
Test::Class1 one(0);
void Test::Class1::Inc()
{
    x++;
}
Test::Class1::Class1(int i)
{
    x = i;
}

int Test::F1()
{
    //extern Test::Class1 one;  
    one.Inc();
    return one.x;
}

I get an undefined reference to Test:one in the F1 function. If I add the extern Test::Class1 one it seems to work. Why is this necessary?

Upvotes: 1

Views: 70

Answers (1)

Christophe
Christophe

Reputation: 73542

This is a little confusing due to the nested class, but it's as simple as:

Test::Class1 Test::one(0);

The following statement in your code, just defines a global objet one that happens to be of a nested type: Test::Class1 :

Test::Class1 one(0);

If it wasn't of a nested type, you'd immediately have noticed the missing qualifier ;-)

Upvotes: 1

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