10

20

Code Understanding

int x,y;  //Global variables declared so that this demo allows them to use from different functions.
class C { //Class C declared
public:
C(){ x=10;}  //Default Constructor sets x as 10.
C(C& D) { x=20;} //Copy Constructor sets x as 20.
};

void func(C E){ } //Function where object E of type C is passed as value.  Function doesn’t perform any job. It will just depict use of copy constructor as object has been passed as value here.

int main(){
C c1;    //c1 is an object based on C, so just default constructor would be called.
cout<<x<<endl; //This prints 10 as default constructor has set x as 10.
func(c1);  //Actual function call with object of C which is c1. Now copy constructor would be called.
cout<<x<<endl; //This would print 20 as copy constructor has now been called.
return 0;
}

Notes

• Copying copy constructor can be called in many other situations like
  – Creating copy of an object.
  – When Object is called by value to a function.
  – When Object is returned from a function.
  – When temporary objects are created.

Common Errors

• If function calls object by reference like this void func(C& E){ } then only normal constructor would run and value 10 10 would be printed.

Suggested Filename(s): objpassedasvalue.cpp,objpval.cpp