operator overloading

[manishanibhwani]

in the following code how does the compiler comes to know that it has to call the postfix function

class Digit
{
private:
    int m_nDigit;
public:
    Digit(int nDigit=0)
    {
        m_nDigit = nDigit;
    }

    Digit& operator++(); // prefix
    Digit& operator--(); // prefix

    Digit operator++(int); // postfix
    Digit operator--(int); // postfix

    int GetDigit() const { return m_nDigit; }
};

Digit& Digit::operator++()
{
    // If our number is already at 9, wrap around to 0
    if (m_nDigit == 9)
        m_nDigit = 0;
    // otherwise just increment to next number
    else
        ++m_nDigit;

    return *this;
}

Digit& Digit::operator--()
{
    // If our number is already at 0, wrap around to 9
    if (m_nDigit == 0)
        m_nDigit = 9;
    // otherwise just decrement to next number
    else
        --m_nDigit;

    return *this;
}

Digit Digit::operator++(int)
{
    // Create a temporary variable with our current digit
    Digit cResult(m_nDigit);

    // Use prefix operator to increment this digit
    ++(*this);             // apply operator

    // return temporary result
    return cResult;       // return saved state
}

Digit Digit::operator--(int)
{
    // Create a temporary variable with our current digit
    Digit cResult(m_nDigit);

    // Use prefix operator to increment this digit
    --(*this);             // apply operator

    // return temporary result
    return cResult;       // return saved state
}

int main()
{
    Digit cDigit(5);
    ++cDigit; // calls Digit::operator++();
    cDigit++; // calls Digit::operator++(int);

    return 0;
}

i know my doubt may is wierd but i m totally confused with the concept that compiler calls prefix func when we write ++ob and calls postfix func when we write ob++...how does compiler gets to know which func to call???does ob++ means we are calling operator++(int) fun ...if yes,then why???

[Ancient Dragon]

The ++ operator doesn't know the difference, the compiler determines the difference based on where the ++ operator is used, such as ++i or i++. And in some cases it won't matter whether its post or prefix. The code inside the operator function should not care one way or the other.

[manishanibhwani]

sir but how does the compiler gets to know that if i m writing ob++ then it has to call the func operator++(int)...

[Ancient Dragon]

In your example ob must be an int. For ob++ the ob int is evaluated first, then when that is done it calls the ++ operator (either the default c++ operator or the one in your program that you wrote).

[admin1982]

based on the parameter passed in postfix,compiler internally treats as postfix