How to keep static const variable as a member of a class

Question

Hi,

I want to keep a static const variable as a member of class. Is it possible to keep and how can i initilize that variable.

Some body helped by saying this

 QString <ClassName>::ALARM_ERROR_IMAGE = "error.png";

http://stackoverflow.com/questions/3698446/initilizing-value-for-a-const-data

I tried like this

in CPP class i write

static  QString ALARM_WARNING_IMAGE ;

In constructor i write

ALARM_WARNING_IMAGE        = "warning.png";

But not working... Please help by giving some hints

Answer 1

Try:

QString ClassName::ALARM_WARNING_IMAGE = "warning.png";

Answer 2

Only const static integral data members are allowed to initialized inside a class or struct.

Answer 3

Here is the basic idea:

struct myclass{
 //myclass() : x(2){}      // Not OK for both x and d
 //myclass(){x = 2;}       // Not OK for both x and d
 static const int x = 2;   // OK, but definition still required in namespace scope
                               // static integral data members only can be initialized
                               // in class definition
     static const double d;    // declaration, needs definition in namespace scope,
                               // as double is not an integral type, and so is
                               // QSTRING.
     //static const QString var; // non integral type
};

const int myclass::x;             // definition
const double myclass::d = 2.2;    // OK, definition
// const QString myclass::var = "some.png";

int main(){
}

Answer 4

Outside of any function in the source file write:

const QString ClassName::ALARM_WARNING_IMAGE = "warning.png";

Header:

class ClassName {
  static const QString ALARM_WARNING_IMAGE;
};

Also, don't write anything in the constructor. This would initialize the static variable everytime ClassName is instantiated ... which does not work, because the variable is const ... bad idea so to speak. consts can only be set once during declaration.