C++程序開發(fā)中我們常用std::sort函數(shù)對(duì)一個(gè)vector數(shù)組進(jìn)行排序，但是某些情況下會(huì)產(chǎn)生crash的情況，比如下面的代碼：

#include <iostream>
#include <algorithm>
#include <vector>

struct Node {
    int id;
    int value;
};

int main()
{
    std::vector<Node> allNodes;

    allNodes.push_back({0, 100});
    allNodes.push_back({1, 200});
    allNodes.push_back({2, 100});
    
    // 錯(cuò)誤的寫法
    std::sort(allNodes.begin(), allNodes.end(), [] (Node& a, Node& b)->bool {
        return (a.value <= b.value);
    });

    for (auto& it : allNodes) {
        std::cout << "id = " << it.id << ", value = " << it.value << std::endl;
    }

    return 0;
}

究其原因是sort函數(shù)要滿足strict weak ordering的要求，即當(dāng)在比較函數(shù)中比較兩個(gè)對(duì)象時(shí)，如果比較條件完全一樣，此時(shí)一定要返回false。
關(guān)于strict weak ordering的解釋，見：https://stackoverflow.com/questions/979759/operator-and-strict-weak-ordering/981299#981299

所以上述代碼要修改比較函數(shù)的實(shí)現(xiàn)即可：

#include <iostream>
#include <algorithm>
#include <vector>

struct Node {
    int id;
    int value;
};

int main()
{
    std::vector<Node> allNodes;

    allNodes.push_back({0, 100});
    allNodes.push_back({1, 200});
    allNodes.push_back({2, 100});

    // 正確的寫法
    std::sort(allNodes.begin(), allNodes.end(), [] (Node& a, Node& b)->bool {
        if (a.value != b.value) {
            return (a.value < b.value);
        }
        return false;
    });

    for (auto& it : allNodes) {
        std::cout << "id = " << it.id << ", value = " << it.value << std::endl;
    }

    return 0;
}