Question

I have run into this situation I find really tricky. I have 2 classes: time12 and time24 which maintain time on a 12 hr and 24 hr basis respectively. Both of them are supposed to have individual conversion functions to handle conversions to the other type. But if I declare time 12 first, then the “time24” in the prototype of the conversion function will be undefined as the time24 class will be declared later. So what do I do now? I can’t even only declare it inside and define it after the 2nd class. So now what?

class time12
{
 operator time24()  //time24 is undefined at this stage
 {

 }
};

class time24
{

};

Answer 1

Normally in c++ you have 2 types of files, .h and .cpp. Your .h file is your declaration, and .cpp is your definition.

Example:

convtime.h:

#ifndef CONVTIME_H_ //this is to prevent repeated definition of convtime.h
#define CONVTIME_H_

class time24; //for the operator in class12

class time12
{
public:
    time12(int); //constructor
    operator time24();
private:
    //list your private functions and members here
}

class time24
{
public:
    time24(int); //constructor
private:
    //list your private functions and members here
}

#endif //CONVTIME_H_

convtime.cpp:

#include "convtime.h"

//constructor for time12
time12::time12(int n)
{
    //your code
}

//operator() overload definition for time12
time24 time12::operator()
{
    //your code
}

//constructor for time24
time24::time24(int n)
{
    //your code
}