Question

I am having a problem accessing a static const variable defined in my class private member variable section. Specifically, the code written below can output the variable within the constructor, but when I try to access it through an accessor function, I get an error discussed below. If anyone knows why I would appreciate your help.

#include <iostream>
using namespace std;

class TestStaticVariables
{
 // Private member variable:
 static const double static_double_variable;
public:
 // Constructor:
 TestStaticVariables()
 {
  // Initialization:
  static const double static_double_variable = 20.0;
  cout << static_double_variable;
 }
 // Member Function:
 void test();
};

void TestStaticVariables::test()
{

When this next line is uncommented I get the following error message:

Line Location Tool:0: “TestStaticVariables::static_double_variable”, referenced from:

 //cout << static_double_variable;
}

int main(int argc, char* const argv[])
{

 TestStaticVariables test_instance;

 return 0;
}

Answer 1

Try initializing the variable outside the class definition, here is a working example:

#include <iostream>

class Foo {
    static const double _bar;

public:
    Foo();

    void Bar();
};

const double Foo::_bar = 20.0;

Foo::Foo() {
    std::cout << Foo::_bar << std::endl;
}

void Foo::Bar() {
    std::cout << Foo::_bar << std::endl;
}

int main( int argc, char *argv[] ) {
    Foo f;
    f.Bar();

    return 0;
}