Question

我无法理解在cygwin shell中编译此代码时收到的错误消息。消息很长，但在这1000行错误的中间某处说：

没有匹配的运营商＆lt;

这是什么意思？这是我的代码：

#include <iostream>
#include <string>
#include <set>
#include <algorithm>
#include <iterator>

using namespace std;

struct Grade{
 string id;
 int score;

  bool operator() (Grade& a, Grade& b){
        return a.id < b.id;   
    } 
};  

int main()
{   
    Grade g;
    set<Grade> gs;

    g.id = "ABC123";
    g.score = 99;
    gs.insert(g);

    g.id = "BCD321";
    g.score = 96;
    gs.insert(g);

    for(auto it : gs)
        cout << it.id << "," << it.score;

    return 0;
}

Answer 1

设置要求其元素类型以定义小于运算符。见http://www.cplusplus.com/reference/set/set/?kw=set

您可以像这样定义（在成绩定义之后）：

bool operator< (const Grade& a, const Grade& b){
    return a.id < b.id;
}

Answer 2

std::set以排序顺序存储其元素，这要求其元素类型为其定义operator <。在这种情况下，您需要为operator <类型定义Grade。

bool operator < (const Grade& grade1, const Grade& grade2)
{
   return grade1.score < grade2.score;  // or other method of determining
                                        // if a grade is less than another
}

或者如果你想在结构本身中定义它：

bool operator < ( const Grade& grade2) const
{
    return score < grade2.score;  // or other method of determining
                                    // if a grade is less than another
}

Answer 3

如果您重载std::set<Grade>的{{1}}功能，则可以创建operator<()。可以使用成员函数或非成员函数来定义函数。

无论采用哪种方法，都必须定义函数，使得LHS和RHS都可以是Grade个对象。

会员职能方法：

const

非会员职能方法：

struct Grade{
   string id;
   int score;

   bool operator<(Grade const& rhs) const
   {
      return this->id < rhs.id;   
   }
};

Answer 4

感谢大家的帮助，我见过很多解决方案，这是我的代码，它按升序对ID进行排序

#include <iostream>
#include <string>
#include <set>
#include <algorithm>
#include <iterator>

using namespace std;

struct Grade{
 string id;
 int score;

 bool operator< (const Grade& g) const {

    return this->id < g.id;
 }
}; 


int main()
{   
    Grade g;
   set<Grade> gs;

    g.id = "ABC123";
    g.score = 99;
    gs.insert(g);

    g.id = "BCD321";
    g.score = 96;
   gs.insert(g);

    for(auto it : gs)
        cout << it.id << "," << it.score << endl;; 

    return 0;

Answer 5

以下是正确编译的更新代码。＆＃34;运营商的问题＆lt;＆＃34; for std::set已经解决了：

#include <iostream>
#include <string>
#include <set>
#include <algorithm>
#include <iterator>

using namespace std;

struct Grade{
   string id;
   int score;

    bool operator<(const Grade& that) const
    {
        return this->score < that.score;   
    } 

    bool operator() (Grade& a, Grade& b){
        return a.id < b.id;   
    } 
};  

int main() {
    Grade g;
    set<Grade> gs;

    g.id = "ABC123";
    g.score = 99;
    gs.insert(g);

    g.id = "BCD321";
    g.score = 96;
    gs.insert(g);

    for(auto it : gs)
        cout << it.id << "," << it.score;

    return 0;
}

此示例代码不会编译

5 个答案: