Unresolved external symbol when using static

Question

I am new to c++. I started now playing with classes and I am having a noob problem with statics.

class Test
{
public:
    Test(){};
    ~Test(){};
    static void test();
    static Helper* helper;
};

void Test::test()
{
    Object obj = Test::helper->getObject();
    //...
}

When I try to compile it gives the error:

main.obj : error LNK2001: unresolved external symbol "public: static class Helper* Test::helper" (?helper@Test@@2PAVHelper@@A)

What is wrong with my code?

Answer 1

The first answer is correct. The reason behind this is that you need to allocate memory for static objects outside the class definition. If you define the the class in a header file, and include it in several cpp files, the compiler doesn't know where and how you want to create the object that 'helper' points to.

Answer 2

you need to define Test::helper. Write something like this outside the class:

Helper* Test::helper = new Helper;