overloading of the operator++()

Question

How can I overload operator++ in two different ways (for a++ and ++a)?

Answer 1

The difference lies in whether you define a operator ++ without or with a (dummy) parameter.

Cited from the relevant article on this subject in the C++ FAQ (go there for more details):

class Number {
public:
    Number& operator++ ();     // prefix ++
    Number  operator++ (int);  // postfix ++
}; 

Answer 2

Read this: http://www.parashift.com/c++-faq-lite/operator-overloading.html#faq-13.14

Answer 3

Declare like so:

class A
{
public:
    A& operator++();    //Prefix (++a)
    A operator++(int); //Postfix (a++)

};

Implement properly - do not mess with what everyone knows they do (increment then use, use then increment).

Answer 4

Should look like this:

class Number 
{
    public:
        Number& operator++ ()     // prefix ++
        {
           // Do work on this.
           return *this;
        }

        // You want to make the ++ operator work like the standard operators
        // The simple way to do this is to implement postfix in terms of prefix.
        //
        Number  operator++ (int)  // postfix ++
        {
           Number result(*this);   // make a copy for result
           ++(*this);              // Now use the prefix version to do the work
           return result;          // return the copy (the old) value.
        }
}; 

Answer 5

You have two ways to overload the two (prefix/postfix) ++ operators for a type T:

Object method:

This is the easiest way, using "common" OOP idiom.

class T
{
    public :
        T & operator++() // ++A
        {
            // Do increment of "this" value
            return *this ;
        }

        T operator++(int) // A++
        {
           T temp = *this ;
           // Do increment of "this" value
           return temp ;
        }
} ;

Object non-member function:

This is another way to do this: As long as the functions are in the same namespace as the object they are referring too, they will be considered when the compiler will search for a fonction to handle ++t ; or t++ ; code:

class T
{
    // etc.
} ;


T & operator++(T & p_oRight) // ++A
{
   // Do increment of p_oRight value
   return p_oRight ;
}

T operator++(T & p_oRight, int) // A++
{
   T oCopy ;
   // Copy p_oRight into oCopy
   // Do increment of p_oRigh value
   return oCopy ;
}

It is important to remember that, from a C++ viewpoint (including a C++ compiler viewpoint), those non-member functions are still part of T's interface (as long as they are in the same namespace).

There are too potential advantages of the non-member function notation:

• If you manage to code them without making them friend of T, then you increased the encapsulation of T
• you can apply this even to classes or structures whose code you don't own. This is a non-intrusive way to enhance the interface of an object without modifying its declaration.