Example
If no ordering function is passed, std::sort will order the elements by calling operator< on pairs of elements, which must return a type contextually convertible to bool (or just bool). Basic types (integers, floats, pointers etc) have already build in comparison operators.
We can overload this operator to make the default sort call work on user-defined types.
// Include sequence containers
#include <vector>
#include <deque>
#include <list>
// Insert sorting algorithm
#include <algorithm>
class Base {
public:
// Constructor that set variable to the value of v
Base(int v): variable(v) {
}
// Use variable to provide total order operator less
//`this` always represents the left-hand side of the compare.
bool operator<(const Base &b) const {
return this->variable < b.variable;
}
int variable;
};
int main() {
std::vector <Base> vector;
std::deque <Base> deque;
std::list <Base> list;
// Create 2 elements to sort
Base a(10);
Base b(5);
// Insert them into backs of containers
vector.push_back(a);
vector.push_back(b);
deque.push_back(a);
deque.push_back(b);
list.push_back(a);
list.push_back(b);
// Now sort data using operator<(const Base &b) function
std::sort(vector.begin(), vector.end());
std::sort(deque.begin(), deque.end());
// List must be sorted differently due to its design
list.sort();
return 0;
}
