How to declare a static const char* in your header file?

Question

I\'d like to define a constant char* in my header file for my .cpp file to use. So I\'ve tried this:

private:
    static const char *SOMETHING = \"sommething\";         


        

Answer 1

The error is that you cannot initialize a static const char* within the class. You can only initialize integer variables there.

You need to declare the member variable in the class, and then initialize it outside the class:

// header file

class Foo {
    static const char *SOMETHING;
    // rest of class
};

// cpp file

const char *Foo::SOMETHING = "sommething";

If this seems annoying, think of it as being because the initialization can only appear in one translation unit. If it was in the class definition, that would usually be included by multiple files. Constant integers are a special case (which means the error message perhaps isn't as clear as it might be), and compilers can effectively replace uses of the variable with the integer value.

In contrast, a char* variable points to an actual object in memory, which is required to really exist, and it's the definition (including initialization) which makes the object exist. The "one definition rule" means you therefore don't want to put it in a header, because then all translation units including that header would contain the definition. They could not be linked together, even though the string contains the same characters in both, because under current C++ rules you've defined two different objects with the same name, and that's not legal. The fact that they happen to have the same characters in them doesn't make it legal.