Unresolved external symbol in C++, error LNK1120 and LNK2001

Question

I fail to understand as why I get LNK1120: Unresolved externals and LNK2001: Unresolved external symbol error messages for the following code in C++

class base
{
public:
    static int x;
    void fun()
    {
       base::x = 10;
       cout << base::x;
    }
};

int main()
{
    base b;
    b.fun();
    return 0;
}

Same code works if I remove _static_, so seems like it has to do something with static class member — Aniruddha, Sep 14 '19 at 16:06
Skip down to answer two in the duplicate, specifically **static data members must be defined outside the class in a single translation unit** — user4581301, Sep 14 '19 at 16:36

score 1 · Accepted Answer · answered Sep 14 '19 at 16:08

When you declare a static member in a class, you have to also provide a definition outside the class declaration; like this:

class base
{
public:
    static int x; // DECLARES the variable
    void fun()
    {
       x = 10; // You don't need the base:: prefix inside the class!
       cout << x;
    }
};
int base::x = 0; // DEFINES the variable

score 0 · Answer 2 · answered Sep 14 '19 at 16:09

0

You have only declared x inside the class. Since it's a static variable you must allocat it's memory outside the class scope.

Just add: base::x = 0; After you close the base class.

answered Sep 14 '19 at 16:09

Evgeny Neiterman

9
1

2

You mean `int base::x = 0;` – Sep 14 '19 at 16:11

Unresolved external symbol in C++, error LNK1120 and LNK2001

2 Answers2

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