g++.exe says undefined reference to static member variable

[SirEnder125]

Hello, g++ doesn't seem to like this code:

#include <iostream>

class object
{
public:
    object()
    {
        obj_count += 1;
        std::cout << "Object count: " << obj_count << '\n';
    }
	
	int val;
    static int obj_count;
};

void Func(object o)
{
    std::cout << "Func called.\n";
}

int main()
{
    object o;
    Func(o);

    return 0;
}

Not one of my better codes, it's just to test some stuff.

EDIT:
This code works:

 #include <iostream>

class object
{
public:
    object()
    {
        obj_count += 1;
        std::cout << "Object count: " << obj_count << '\n';
    }
    
    int val = 0;
    static int obj_count;
};

int object::obj_count = 0;

void Func(object o)
{
    std::cout << "Func called.\n";
}

int main()
{
    object o;
    Func(o);

    return 0;
}

Weird what one line can do to a code...

[JLBorges]

Define the static member (in some .cpp file)

#include <iostream>

class object
{
public:
    object()
    {
        obj_count += 1;
        std::cout << "Object count: " << obj_count << '\n';
    }
	
	int val;
    static int obj_count;
};

void Func(object)
{
    std::cout << "Func called.\n";
}

int main()
{
    object o;
    Func(o);

    return 0;
}

int object::obj_count = 0 ; // **** define it **** 

http://coliru.stacked-crooked.com/a/a0a234b51157d2ea

[SirEnder125]

Thanks! :P