Understand Copy Constructor
compile in windows: cl /EHsc main.cpp

Output:

C:\c++Test>cat HowMany.out
after construction of h: object count = '1'
x argument inside f(): object count = '1'
~HowMany(): object count = '0'
after call to f(h): object count = '0'
~HowMany(): object count = '-1'
~HowMany(): object count = '-2'

Source Code

#include 
#include 
using namespace std;

ofstream out("HowMany.out");

class HowMany {
  static int count;
public:
  HowMany()
  {
     count++ ;
  }
  static void print(const string &msg="")
  {
     if (msg.size() != 0)
     {
        out << msg << ": " ;
     }
     out << "object count = '" << count << "'" << endl;
  }
  ~HowMany()
  {
     count--;
     print("~HowMany()");
  }
};

int HowMany::count = 0;

HowMany f(HowMany x) {
  x.print("x argument inside f()");
  return x;
}

void main()
{
  HowMany h;
  HowMany::print("after construction of h");
  HowMany h2 = f(h);
  HowMany::print("after call to f(h)");
}

- posted by Pop @ 9:52 AM