结构体排序的三种方式

方式1 lambda表达式

使用lambda表达式来完成sort()函数的第3个参数，十分优雅，强烈推荐。

语法为

[](Student a, Student b){return a.ChineseGrade >= b.ChineseGrade;}

完整程序如下，

#include 
#include 

using namespace std;

struct Student
{
    string name;
    int MathGrade;
    int ChineseGrade;
};


int main()
{

    Student students[5];
    students[0] = {"赵", 10, 20};
    students[1] = {"钱", 20, 40};
    students[2] = {"孙", 50, 30};
    students[3] = {"李", 40, 10};
    students[4] = {"王", 30, 50};
    
    //语文成绩大的学生排在前面，结构体中的变量ChineseGrade
    sort(students, students+5, [](Student a, Student b){return a.ChineseGrade >= b.ChineseGrade;});
    
    for(int i = 0; i < 5; i++)
        cout << "name = " << students[i].name << ", mathgrade = " << students[i].MathGrade << ", chinesegrade = " << students[i].ChineseGrade << endl;
    
    return 0;
}

程序输出为，

name = 王, mathgrade = 30, chinesegrade = 50
name = 钱, mathgrade = 20, chinesegrade = 40
name = 孙, mathgrade = 50, chinesegrade = 30
name = 赵, mathgrade = 10, chinesegrade = 20
name = 李, mathgrade = 40, chinesegrade = 10

方式2 重载小于号

在结构体内部重载小于号bool operator < (const Student& tmp) const，

#include 
#include 

using namespace std;

struct Student
{
    string name;
    int MathGrade;
    int ChineseGrade;
    //重载小于号，语文成绩大的学生排在前面，结构体中的变量ChineseGrade 
    bool operator< (const Student& tmp) const
    {
        return ChineseGrade > tmp.ChineseGrade;
    }
};


int main()
{

    Student students[5];
    students[0] = {"赵", 10, 20};
    students[1] = {"钱", 20, 40};
    students[2] = {"孙", 50, 30};
    students[3] = {"李", 40, 10};
    students[4] = {"王", 30, 50};
    
    sort(students, students+5);
    
    for(int i = 0; i < 5; i++)
        cout << "name = " << students[i].name << ", mathgrade = " << students[i].MathGrade << ", chinesegrade = " << students[i].ChineseGrade << endl;
    
    return 0;
}

输出为，

name = 王, mathgrade = 30, chinesegrade = 50
name = 钱, mathgrade = 20, chinesegrade = 40
name = 孙, mathgrade = 50, chinesegrade = 30
name = 赵, mathgrade = 10, chinesegrade = 20
name = 李, mathgrade = 40, chinesegrade = 10

双条件排序，代码示例如下：

struct projectionRoadboundary {
    double minoffset = 0.0;
    double maxoffset = 0.0;
    int markingid = 0;

    //按照minoffset从小到大排序，如果minoffset相近，则按照maxoffset从小到大排序
    bool operator<(const projectionRoadboundary& tmp) const {
        return minoffset < tmp.minoffset || (abs(minoffset - tmp.minoffset) <= 1e-6 && maxoffset < tmp.maxoffset);
    }
};

方式3 实现cmp()函数

在结构体外写bool cmp(Student a, Student b)函数，

#include 
#include 

using namespace std;

struct Student
{
    string name;
    int MathGrade;
    int ChineseGrade;
};

bool cmp(Student a, Student b)
{
    return a.ChineseGrade > b.ChineseGrade;
}


int main()
{
    Student students[5];
    students[0] = {"赵", 10, 20};
    students[1] = {"钱", 20, 40};
    students[2] = {"孙", 50, 30};
    students[3] = {"李", 40, 10};
    students[4] = {"王", 30, 50};
    
    //语文成绩大的学生排在前面，结构体中的变量ChineseGrade
    sort(students, students+5, cmp);
    
    for(int i = 0; i < 5; i++)
        cout << "name = " << students[i].name << ", mathgrade = " << students[i].MathGrade << ", chinesegrade = " << students[i].ChineseGrade << endl;
    
    return 0;
}

输出为，

name = 王, mathgrade = 30, chinesegrade = 50
name = 钱, mathgrade = 20, chinesegrade = 40
name = 孙, mathgrade = 50, chinesegrade = 30
name = 赵, mathgrade = 10, chinesegrade = 20
name = 李, mathgrade = 40, chinesegrade = 10