Static member variable

[Slazer]

If I have defined this in my *.cpp file

  const string A::B = "foo";

does it mean that I have to define variable B as static member of class A in my *.h file?

[kevinkjt2000]

In *:
.h

class A {   
private:      
  static const string B;
};

In *.cpp:
const string A::B = "foo";

[S6k9GNh0]

It could also be that A is a namespace.

[vlad from moscow]

@Slazer

If I have defined this in my *.cpp file



const string A::B = "foo";


does it mean that I have to define variable B as static member of class A in my *.h file?

static data members are declared in class definitions.

[kevinkjt2000]

@computerquip: The OP said

class A

.
@vlad from moscow: Did you read my post?

[chenshuiluke]

Well, I just tested it without the static storage class and it seems to work fine. Sooo does that answer your question?
*.h:

class AnotherTest
{
private:
  const std::string B;
  AnotherTest();
  ~AnotherTest();
};

*.cpp:

#include "AnotherTest.h"
#include <string>
AnotherTest::AnotherTest()
{
const std::string  B = "stuff";
}

[vlad from moscow]

Variable B defined as a data member in the class

class AnotherTest
{
private:
  const std::string B;
  AnotherTest();
  ~AnotherTest();
};

and local variable B defined inside the constructor

#include "AnotherTest.h"
#include <string>
AnotherTest::AnotherTest()
{
const std::string  B = "stuff";
}

are two different objects. Data member B is an empty constant string that have storage duration until an object of the class exists. Local variable B inside the constructor has automatic storage duration and is destroyed after the constructor will finish his work.

[keskiverto]

Const data member has to be initialized in the constructor. Each instance of A will have their own B (so each A::B can hold a different value).

If the implementation defines const string A::B = "foo";, then A::B is initialized exactly once, not in constructor, and it will be initialized even if no A is ever created within the program. Therefore, yes, A::B is/should/must be a static member variable.

Static member variable is like a global variable, but has the benefit of being accessible only by those, who can access members of A.