Duplicate:
C++: undefined reference to static class member
If I have a class/struct like this
// header file
class Foo
{
public:
static int bar;
int baz;
int adder();
};
// implementation
int Foo::adder()
{
return baz + bar;
}
This doesn't work. I get an "undefined reference to `Foo::bar'" error. How do I access static class variables in C++?
You must add the following line in the implementation file:
int Foo::bar = you_initial_value_here;
This is required so the compiler has a place for the static variable.
It's the correct syntax, however, Foo::bar must be defined separately, outside of the header. In one of your .cpp files, say this:
int Foo::bar = 0; // or whatever value you want