Why Do I Get an 'Undefined Reference to Static Variable' Error in C and How Can I Fix It Without Using Static Methods?

Undefined Reference to Static Variable in C

When working with static variables in C , developers often encounter the error "undefined reference to static variable." This article explores this issue and provides a solution without using a static method.

Problem:

Consider the following code:

class Helloworld {
  public:
     static int x;
     void foo();
};
void Helloworld::foo() {
     Helloworld::x = 10;
};

This code triggers an "undefined reference" error because the static variable x is referenced in a non-static method foo(), but it lacks a definition.

Solution:

To resolve this issue, it is essential to provide a definition for the static member variable x outside the class definition. This can be achieved as follows:

class Helloworld {
  public:
     static int x;
     void foo();
};

// Define the static variable outside the class
int Helloworld::x = 0;

void Helloworld::foo() {
     Helloworld::x = 10;
};

By specifying the initial value as 0 or leaving it undefined, x will be zero-initialized. Alternatively, a more appropriate initial value can be assigned.

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