Question

Consider the sample program below:

#include <iostream>

using namespace std;

class test
{
   public:
      static const float data;
};

float const test::data = 10;   // Line1


int main()
{
   cout << test::data;
   cout << "\n";

   return 0;
}

Please note the comment Line1 in the sample code.

Questions:

1. Is Line1 doing the initialization of the date member data?
2. Is Line1 the only way to initialize a static const non-integral data member?

Answer 1

Is Line1 doing the initialization of the date member data?

It certainly is, as well as providing the definition of the object. Note that this can only be done in a single translation unit, so if the class definition is in a header file, then this should be in a source file.

Is Line1 the only way to initialize a static const non-integral data member?

In C++03 it was. In C++11, any static member of const literal type can have an initialiser in the class definition. You still need a definition of the member if it’s “odr-used” (roughly speaking, if you do anything that needs its address, not just its value). In this case, the definition again needs to be in a single translation unit, and must not have an initialiser (since there’s already one in the class definition).