C++怎么在类中使用sort，比较函数是非静态成员函数

Question

简易代码如下

#include <iostream>
#include <algorithm>

using namespace std;

struct B {
    int x = 0;
};

class A {
public:
    A() {
        b[0].x = 0;
        b[1].x = 1;
        b[2].x = 2;
        b[3].x = 3;
        b[4].x = 4;
    }

    void test() {
        sort(b, b + 5, cmp);    // 这行报错
        for (int i = 0; i < 5; ++i) {
            cout << b[i].x << endl;
        }
    }

    bool cmp(B b1, B b2) {
        return c[b1.x] > c[b2.x];
    }

private:
    B b[5];
    int c[5] = {11, 22, 33, 44, 55};
};

int main() {
    A testa;
    testa.test();
    system("pause");
    return 0;
}

非静态成员函数参数会自带this，怎么办？

Answer 1

用std::bind

 #include <iostream>
#include <algorithm>
#include <functional>

using namespace std;
using std::placeholders::_1;
using std::placeholders::_2;

struct B {
    int x = 0;
};

class A {
public:
    A() {
        b[0].x = 0;
        b[1].x = 1;
        b[2].x = 2;
        b[3].x = 3;
        b[4].x = 4;
    }

    void test() {
        auto bound_cmp=bind(&A::cmp, this, _1, _2);
        sort(b, b + 5, bound_cmp);
        for (int i = 0; i < 5; ++i) {
            cout << b[i].x << endl;
        }
    }

    bool cmp(B b1, B b2) {
        return c[b1.x] > c[b2.x];
    }

private:
    B b[5];
    int c[5] = {11, 22, 33, 44, 55};
};

int main() {
    A testa;
    testa.test();
        system("pause");
    return 0;
}