C++ operators such as + (addition), < (less than), -- (decrement), << (print) may be redefined. This behavior is termed operator overloading. There may be scenarios where we want to extend how these operators behave to suit a specific context. The example below demonstrates how to overload the -- decrement operator within a class.
#include <iostream>
using namespace std;
class OClass {
private:
int count;
public:
OClass(int cnt){
count = cnt;
}
// prefix decrement operator
void operator--() {
count = count - 3;
}
// postfix decrement operator
void operator--(int) {
count = count - 5;
}
void print() {
cout << "Count: " << count << endl;
}
};
int main() {
OClass obj(4);
// overloaded decrement
--obj;
obj.print();
// overloaded decrement
obj--;
obj.print();
// original decrement
int i = 5;
i--;
cout << "Count: " << i << endl;
return 0;
}In the example above, we overloaded the decrement operator -- to decrement by three or five depending on how the decrementer was called (as a prefix or postfix to the object calling it). You should notice that the operators are all functions and can be re-defined as such. When overloading the decrement operator, the prefix of it is defined as void operator--(), while the postfix version is defined as void operator--(int). Re-defining the decrement operator does not overload the global instantiation of the decrement operator. Only operators can be overloaded, and almost all of them can be overloaded with a few exceptions. You can view a full list here.