Can const member variable of class be initialized in a method instead of constructor?

Question

I have a class and want to create a const int variable but the value for the variable is not available to me in constructor of the class.

In initialization method of the class i get the value. Can I assign it in that method? As I am assigning it only once (as const says) why it isn't working?

Code is as Following [Just a ProtoType] :

File : A.h

Class A
{
  private :
  const long int iConstValue;

  public :
  A();
  initClassA();
}

File : A.cpp

A::A()
{
 //CanNot initialize iConstValue (Don't have it)
}

A::initClassA(some params)
{
 // calculation according to params for iConstValue
 iConstValue = (some value)
}

This is not working. Somebody has any Solutions?

NOTE : I Can not get value for iconstValue in constructor by any way as there are some restriction. So Please don't suggest to do that.

Answer 1

A small example:

class A
{
public:
  A():a(initial_value_of_a()) {}

private:
  const int a;
  int initial_value_of_a() { return 5; /* some computation here */ };
};