Question

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What does it mean to have an undefined reference to a static member?

I have a static class as follows:

.h file

class c1 {
    public:
    static int disconnect();
    private:
    static bool isConnected;
    };

.cpp file

#include c1.h

int c1::disconnect()
{
    c1::isConnected = false;
    return 0;
}

However when I compile, there is an error

undefined reference to `c1::m_isConnected'

Please help!

Answer 1

You have to provide an actual object instance for the static class members. Add the following to your .cpp file:

 bool c1::isConnected;

To initialize it to a specific value, add an initializer:

 bool c1::isConnected = false;

(By the way, classes in C++ cannot be static. Classes are just types. Only class members can be static.)