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Could someone help me initialse the class constructor

ClassA{
public:
        ClassA(int kg);
      virtual ~ClassA();
private:
      int kk;
};
ClassA::ClassA(int kg) {
      kk = kg;
}

ClassA::~ClassA() {
}
class classB {
public:
      classB();
      virtual ~classB();  
        ClassA ca;
};

classB::classB()//I am getting error at this line
{
     //how to initialse the constructor of B
}

classB::~classB() {

}
0
pvinodp
Asked:
pvinodp
2 Solutions
 
ZoppoCommented:
Hi pvinodp,

the problem is the constructor of ClassA expects an int as argument, but the way it's implemented it can only be used when there's a default constructor. You can either add a default constructor to ClassA or change the existing constructorto take a default argument or initialize 'ca' in classB's constructor using an initialization list, i.e.:
// method 1: implement a default constructor
class ClassA
    ClassA(int kg=0); // added default argument so this becomes a default constructor
    virtual ~ClassA();
private:
      int kk;
};

ClassA::ClassA(int kg) {
      kk = kg;
}

// method 2: initialize 'ca'
classB::classB()
: ca( 5 ) // using 5 for just as sample
{
}

Open in new window

Hope this helps,

ZOPPO
0
 
phoffricCommented:
Sometimes you are not able to modify ClassA as it may be written by a third party. But if you can modify classB, then you could take a couple of approaches. One approach is to provide a default value for classA in the classB constructor initialization list (as Zoppo as shown). Another approach is to add another classB constructor that takes an arg that can be used for the ca initialization. Both approaches are shown below with no functional change to ClassA.
#include <iostream>
using namespace std;

class ClassA {
public:
      ClassA(int kg) : kk(kg) {}
      virtual ~ClassA() {}
      int get_kk() {return kk;}
private:
      int kk;
};


class classB {
public:
      classB()  : ca(12) {}
      classB(int Bkg) : ca(Bkg) {} // add constructor to provide value for ClassA
      virtual ~classB() {}  
      ClassA ca;
};


int main() {
   ClassA myA(10);
   classB myClassB;
   classB myClassB2(22);

   cout << myA.get_kk() << endl;
   cout << myClassB.ca.get_kk() << endl;
   cout << myClassB2.ca.get_kk() << endl;
}

Open in new window

0
 
pvinodpAuthor Commented:
thanks for your answers
0
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