Defining New C++ Operators

Ndimangwa · #1 08-Apr-2009, 03:14

I C++ we can overload an operators, that is fine!!

My question is how do I define a new operator apart from overloading the ones existing?
Including how to set rules and principles of how the operator manipulates its operands?

Thank you much!!!!

Mexican Bob · #2 08-Apr-2009, 05:41

Quote:

Originally Posted by Ndimangwa

I C++ we can overload an operators, that is fine!!

My question is how do I define a new operator apart from overloading the ones existing?
Including how to set rules and principles of how the operator manipulates its operands?

Thank you much!!!!

Consider the following:

CPP / C++ / C Code:

#ifndef Money_h_
#define Money_h_

#include <cstdlib>
#include <iostream>
#include <string>

class Money
{
public:
    Money();
    Money(Money const& rhs);
    Money& operator=(Money const& rhs);
    ~Money(); 

    Money(std::string const& amount);

#if _UNICODE
    Money(const wchar* amount);
#else
    Money(const char* amount);
#endif

    bool operator!=(Money const& rhs) const;
    bool operator==(Money const& rhs) const;
    bool operator<(Money const& rhs);
    bool operator>(Money const& rhs);
    bool operator<=(Money const& rhs);
    bool operator>=(Money const& rhs);

    Money& operator+(Money const& rhs);
    Money& operator-(Money const& rhs);
    Money& operator/(Money const& rhs);
    Money& operator*(Money const& rhs);

    Money& operator-=(Money& rhs);
    Money& operator+=(Money& rhs);

#if _UNICODE
    const wchar getCurrencySymbol() const;
    void setCurrencySymbol(const wchar symbol);
#else
    const char getCurrencySymbol() const;
    void setCurrencySymbol(const char symbol);
#endif
    friend std::ostream& operator<<(std::ostream& os, Money const& rhs);
    friend std::istream& operator>>(std::istream& is, Money& rhs);
protected:
private:
    int   m_lodp; // left of decimal point
    int   m_rodp; // right of decimal point
#if _UNICODE
    wchar m_currency_symbol;
#else
    char  m_currency_symbol;
#endif
};


#endif

There are declarations for operators that would be inserted by the compiler if omitted and there are declarations for operators for which the compiler is unable to give any reasonable implementation.

The operator declarations are as follows:

assignment copy operator

inequality operator
equality operator
less-than comparison operator
greather-than comparison operator
less-than-or-equal-to comparison operator
greather-than-or-equal-to comparison operator

basic arithmetic operators

operators for assignment by addition and substraction

and finally, streaming operators for I/O.

Notably missing are ++ and -- operator declarations. At first glance, they appear to be relevant, but upon further investigation, their usage would be unclear.

Hopefully this will give you an idea of how to use operators more effectively. One should carefully examine the implementation such that expected behavior of defined operators is intuitive and easily anticipated. As in the case of not defining ++ and -- operators, since we do not easily know from which side of the decimal point they would work, any choice for them appears to be wrong in at least one or more expectations of their behaviors.

However, if we were declaring a class called Integer, we would then probably expect to see both ++ and -- declarations for postfix and prefix versions of these operators as the behavior of these would be easily anticipated by the user and therefore have an appropriate implementation.

See: operator-overloading for more info.

MxB

davekw7x · #3 08-Apr-2009, 09:00

Quote:

Originally Posted by Ndimangwa

My question is how do I define a new operator apart from overloading the ones existing?

Overloading gives new meaning to the standard operators defined by the language.

In standard C or C++ you can not create new operators different from the ones defined in the language. Period. Full stop.

Regards,

Dave

siddhant3s · #4 21-Apr-2009, 05:13

Well, Bjarne Stroustup gives a good explaination why he didn't allowed "Home made operators" in C++. Here it is http://www.research.att.com/~bs/bs_faq2.html#overload-operator
Hope this reading will convince you

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Defining New C++ Operators

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