You overload a unary operator with either a nonstatic member function that has no parameters, or a nonmember function that has one parameter. Suppose a unary operator @ is called with the statement @t, where t is an object of type T. A nonstatic member function that overloads this operator would have the following form:
return_type operator@()
A nonmember function that overloads the same operator would have the following form:
return_type operator@(T)
An overloaded unary operator may return any type.
The following example overloads the ! operator:
#include <iostream>
using namespace std;
struct X { };
void operator!(X) {
cout << "void operator!(X)" << endl;
}
struct Y {
void operator!() {
cout << "void Y::operator!()" << endl;
}
};
struct Z { };
int main() {
X ox; Y oy; Z oz;
!ox;
!oy;
// !oz;
}The following is the output of the above example:
void operator!(X) void Y::operator!()The operator function call !ox is interpreted as operator!(X). The call !oy is interpreted as Y::operator!().
(The compiler would not allow !oz because the ! operator has not been defined for class Z.)
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