// custom_exception.cc
#include <iostream>
#include <string>
#include <exception>
#include <math.h>
using namespace std;

class MyException: public std::exception
{
  string Message;
 
  public:
    MyException(const char *msg):Message(msg) {}
    virtual const char* what() const throw() { return Message.c_str(); }
    ~MyException() throw() {}
};

double SafeSqrt(double x) {
  if (x < 0.0)
    throw MyException("MyException: Tried to take sqrt of negative number");
  return sqrt(x);  
}

int main() {
  double x = -4.0, y;
  try {
    y = SafeSqrt(x);
    cout << "The square root of " << x << " is " << y << endl;
  }
  catch (std::exception& ex) { // any std::exception incl. ours!
    cout << ex.what() << endl;
  }
}