◄Up► ◄Contents► ◄Index► ◄Back►
─────C/C++ Language─────────────────────────────────────────────────────────
 
  Keyword:  operator
 
  Syntax:   type operator operator-symbol ( parameter-list )
 
  Summary:  Declares a function specifying what <operator-symbol>
            means when applied to instances of a class. This gives the
            operator more than one meaning, or "overloads" it. The
            compiler distinguishes between the different meanings of
            an operator by examining the types of its operands.
 
  See also: ◄Operators►
            ◄Operator Precedence Table►
 
     Rules of Operator Overloading
 
     ■ You can overload the following operators:
 
          +     -     *     /     %     ^     &     |     ~
          !     =     <     >     +=    -=    *=    /=    %=
          ^=    &=    |=    <<    >>    <<=   >>=   ==    !=
          <=    >=    &&    ||    ++    --    ,     ->    ->*
          ()    []    new   delete
 
     ■ If an operator can be used as either a unary or a binary
       operator, you can overload each use separately.
 
     ■ You can overload an operator using either a nonstatic member
       function or a global function that's a friend of a class.
       A global function must have at least one parameter that is of
       class type or a reference to class type.
 
     ■ If a unary operator is overloaded using a member function, it
       takes no arguments. If it is overloaded using a global function,
       it takes one argument.
 
     ■ If a binary operator is overloaded using a member function, it
       takes one argument. If it is overloaded using a global function,
       it takes two arguments.
 
     Restrictions on Operator Overloading
 
     ■ You cannot define new operators, such as **.
 
     ■ You cannot change the precedence or grouping of an operator,
       nor can you change the numbers of operands it accepts.
 
     ■ You cannot redefine the meaning of an operator when applied to
       built-in data types.
 
     ■ Overloaded operators cannot take default arguments.
 
     ■ You cannot overload any preprocessor symbol, nor can you
       overload the following operators:
 
          .     .*    ::    ?:    :>
 
     ■ The assignment operator has some additional restrictions. It
       can be overloaded only as a nonstatic member function, not as a
       friend function. It is the only operator that cannot be
       inherited; a derived class cannot use a base class's assignment
       operator.
 
     Example
 
     The following stack class overloads the += operator to push a
     value onto a stack and return the new stack.
 
          class Complex
          {
          public:
              Complex( float re, float im );
              Complex operator+( Complex &other );
              friend Complex operator+( int first, Complex &second );
          private:
              float real, imag;
          };
 
          // Operator overloaded using a member function
          Complex Complex::operator+( Complex &other )
          {
              return Complex( real + other.re, imag + other.im );
          };
 
          // Operator overloaded using a friend function
          Complex operator+( int first, Complex &second )
          {
              return Complex( first + second.re, second.im );
          }
                                    -♦-