C++: Bilateral class conversion

Question

Let's say, I have two simple classes: integer with just one int variable in it, and real with double. I'm already done so that

integer a=2016; int b=a;

real a=20.16; double b=a;

working perfectly. Now I have to do the conversion between them, like so:

integer foo; real bar; foo=bar; bar=foo;

Or at least with similar syntax. I know that there will be loss of some data when converting double to int, I'll deal with it. So how can I do that? What and where should I #include and what the methods/operator overloads to write? My project is divided into files main.cpp, integer.h, integer.cpp, real.h, real.cpp. Thanks.

EDIT: The classes looks like:

//integer.h
class integer
{
    private:
        int a;
    public:
        integer();
        integer(int number);
        operator int() const;
};
//integer.cpp
#include "integer.h"

integer::integer(){
    a=0;
}
integer::integer(int number){
    a=number;
}
integer::operator int() const{
    return a;
}
//real.h
class real {
    private:
        double a;
    public:
        real();
        real(double number);
        operator double() const;
};
//real.cpp
#include "real.h"

real::real(){
    a=0;
}
real::real(double number){
    a=number;
}
real::operator double() const{
    return a;
}

you'll need to show us minimal versions of these classes to get a good answer. — Richard Hodges, Sep 14 '16 at 12:48
@erip Doesn't inheritance, in this case, have the [circle-ellipse problem](https://en.wikipedia.org/wiki/Circle-ellipse_problem)? — Ami Tavory, Sep 14 '16 at 12:49
inheritance would be the wrong solution for two classes with dissimilar interfaces. real numbers and integers are absolutely dissimilar. — Richard Hodges, Sep 14 '16 at 12:53

score 2 · Accepted Answer · answered Sep 14 '16 at 12:48

2

You basically have two solutions to your problem:

The first is to write conversion operators that can convert a real object to an integer object, and vice versa.

The other solution is to implement custom constructors and assignment operators to take the other class.

answered Sep 14 '16 at 12:48

Some programmer dude

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I've tried to do like in first example of "Explanation", got "Incomplete type used in nested name specifier". How to do the second variant? – 1valdis Sep 14 '16 at 13:57
@1valdis Only put the conversion operator function ***declarations*** in the class. Then ***define*** (i.e. implement) the function after both classes are fully defined. – Some programmer dude Sep 14 '16 at 14:43
I did declare functions in headers, defined in their .cpp's. Where else should I do that? – 1valdis Sep 14 '16 at 14:50
@1valdis You do remember to add forward declarations of the classes, not including the header files into each other and thereby creating a circular dependency? See e.g. [this simple example on how it could be done](http://ideone.com/JnL92S). – Some programmer dude Sep 14 '16 at 15:13
Yes, I write class real; before class integer{...} and so on. – 1valdis Sep 14 '16 at 15:15

C++: Bilateral class conversion

1 Answers1