12 Overloading [over]

12.4 Overloaded operators [over.oper]

12.4.7 Increment and decrement [over.inc]

1
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An increment operator function is a function named operator++.
If this function is a non-static member function with no non-object parameters, or a non-member function with one parameter, it defines the prefix increment operator ++ for objects of that type.
If the function is a non-static member function with one non-object parameter (which shall be of type int) or a non-member function with two parameters (the second of which shall be of type int), it defines the postfix increment operator ++ for objects of that type.
When the postfix increment is called as a result of using the ++ operator, the int argument will have value zero.113
[Example 1: struct X { X& operator++(); // prefix ++a X operator++(int); // postfix a++ }; struct Y { }; Y& operator++(Y&); // prefix ++b Y operator++(Y&, int); // postfix b++ void f(X a, Y b) { ++a; // a.operator++(); a++; // a.operator++(0); ++b; // operator++(b); b++; // operator++(b, 0); a.operator++(); // explicit call: like ++a; a.operator++(0); // explicit call: like a++; operator++(b); // explicit call: like ++b; operator++(b, 0); // explicit call: like b++; } — end example]
2
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A decrement operator function is a function named operator-- and is handled analogously to an increment operator function.
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Calling operator++ explicitly, as in expressions like a.operator++(2), has no special properties: The argument to operator++ is 2.