为什么std::sort使用这种简单的严格弱排序比较仍然崩溃?[副本]

你的比较器不遵守严格的弱序。

例如: a={2,0,1},b={1,0,2}

对于<b(由于第一 if 在比较器中),但对于b<a(由于第二 如果 在里面)。

由于这不符合比较器的要求 std::sort ,它会导致未定义的行为。

代码崩溃是因为排序的比较函数搞砸了。基本上,它没有遵循std::sort正常工作所需的规则。原来的功能到处都是,有时说一件事更小,有时不是——它超级不一致。

为了解决这个问题,我不得不重写比较部分。现在它先检查第三个数字,然后检查第一个,然后检查第二个。这样更符合逻辑和一致性。

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

void test() {
    std::vector<std::vector<int>> info = {{0,0,999}, {0,1,1000}, {0,2,1001},
                {0,3,1002}, {0,4,1003}, {0,5,1004},
                {0,6,1005}, {0,7,1006}, {1,0,1000},
                {1,1,999}, {1,2,1000}, {1,3,1001},
                {1,4,1002}, {1,5,1003}, {1,6,1004},
                {1,7,1005}, {2,0,1001}, {2,1,1000},
                {2,2,999}, {2,3,1000}, {2,4,1001},
                {2,5,1002}, {2,6,1003}, {2,7,1004},
                {3,0,1002}, {3,1,1001}, {3,2,1000},
                {3,3,999}, {3,4,1000}, {3,5,1001},
                {3,6,1002}, {3,7,1003}, {4,0,1003},
                {4,1,1002}, {4,2,1001}, {4,3,1000},
                {4,4,999}, {4,5,1000}, {4,6,1001},
                {4,7,1002}, {5,0,1004}, {5,1,1003},
                {5,2,1002}, {5,3,1001}, {5,4,1000},
                {5,5,999}, {5,6,1000}, {5,7,1001},
                {6,0,1005}, {6,1,1004}, {6,2,1003},
                {6,3,1002}, {6,4,1001}, {6,5,1000},
                {6,6,999}, {6,7,1000}, {7,0,1006},
                {7,1,1005}, {7,2,1004}, {7,3,1003},
                {7,4,1002},{7,5,1001}};  

    auto cmp = [](const auto& a, const auto& b) {
        if (a[2] != b[2]) return a[2] < b[2];
        if (a[0] != b[0]) return a[0] < b[0];
        return a[1] < b[1];
    };

    std::sort(begin(info), end(info), cmp);

    for (const auto& v : info) {
        std::cout << v[0] << " " << v[1] << " " << v[2] << std::endl;
    }
}

int main() {
    test();
    return 0;
}