How Do You Create a Static Class in C++?

Question

How do you create a static class in C++? I should be able to do something like:

cout << "bit 5 is " << BitParser::getBitAt(buffer, 5) << endl;

Assuming I created the BitParser class. What would the BitParser class definition look like?

Accepted Answer

If you're looking for a way of applying the "static" keyword to a class, like you can in C# for example, then you won't be able to without using Managed C++.

But the looks of your sample, you just need to create a public static method on your BitParser object. Like so:

BitParser.h

class BitParser
{
 public:
  static bool getBitAt(int buffer, int bitIndex);

  // ...lots of great stuff

 private:
  // Disallow creating an instance of this object
  BitParser() {}
};

BitParser.cpp

bool BitParser::getBitAt(int buffer, int bitIndex)
{
  bool isBitSet = false;
  // .. determine if bit is set
  return isBitSet;
}

You can use this code to call the method in the same way as your example code.

Answer 2

Consider Matt Price's solution.

In C++, a "static class" has no meaning. The nearest thing is a class with only static methods and members.
Using static methods will only limit you.

What you want is, expressed in C++ semantics, to put your function (for it is a function) in a namespace.

Must Read

Edit 2011-11-11

There is no "static class" in C++. The nearest concept would be a class with only static methods. For example:

// header
class MyClass
{
   public :
      static void myMethod() ;
} ;

// source
void MyClass::myMethod()
{
   // etc.
}

But you must remember that "static classes" are hacks in the Java-like kind of languages (e.g. C#) that are unable to have non-member functions, so they have instead to move them inside classes as static methods.

In C++, what you really want is a non-member function that you'll declare in a namespace:

// header
namespace MyNamespace
{
   void myMethod() ;
}

// source
namespace MyNamespace
{
   void myMethod()
   {
      // etc.
   }
}

Why is that?

In C++, the namespace is more powerful than classes for the "Java static method" pattern, because:

static methods have access to the classes private symbols
private static methods are still visible (if inaccessible) to everyone, which breaches somewhat the encapsulation
static methods cannot be forward-declared
static methods cannot be overloaded by the class user without modifying the library header
there is nothing that can be done by a static method that can't be done better than a (possibly friend) non-member function in the same namespace
namespaces have their own semantics (they can be combined, they can be anonymous, etc.)
etc.

Conclusion: Do not copy/paste that Java/C#'s pattern in C++. In Java/C#, the pattern is mandatory. But in C++, it is bad style.

How Do You Create a Static Class in C++?

15 Answers

Must Read

Edit 2011-11-11

Why is that?

James H. Sterling