通過過載較少的運算子對序列容器進行排序

如果沒有傳遞排序函式，std::sort 將通過在元素對上呼叫 operator< 來對元素進行排序，這些元素必須返回一個上下文可轉換為 bool 的型別（或者只是 bool）。基本型別（整數，浮點數，指標等）已經在比較運算子中構建。

我們可以過載此運算子以使預設的 sort 呼叫適用於使用者定義的型別。

// 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;
}