How do I solve this std::sort and struct issue?

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hi, this code won't compile correctly using std::sort and a struct.

How do I solve this?

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

struct StudentDataTypes
{
    std::string name{};
    int grade{};
};

int main()
{
    //Ask for Class_Size
    int Class_Size{};
    std::cout << "How big is the class?" << '\n';
    std::cin >> Class_Size;

    //Syntax format
    //std::vector<T> array(size);
    //Intialize a vector for the students called Vector_Student
    //T links to the struct StudentDataTypes
    //size is the Class_Size.
    std::vector<StudentDataTypes> Vector_Student(Class_Size);
    
    //Print Class Size
    std::cout << "There are " << Class_Size << " students." << '\n';

    //Get the Userinputs for the Class
    for (int i = 0; i < Class_Size; ++i)
    {
        std::cout << "Please input the name of Student #" << i + 1 << '\n';
        std::cin >> Vector_Student[i].name;
        std::cout << "Please input the grade of Student #" << i + 1 << '\n';
        std::cin >> Vector_Student[i].grade;
    }
    
    //Sort
    std::sort(Vector_Student.begin(), Vector_Student.end());

    //Print the required output
    for (int j = 0; j < Class_Size; ++j)
    {
        std::cout 
            << Vector_Student[j].name 
            << " got a grade of " 
            << Vector_Student[j].grade << '\n';
    }
    
    return 0;
}

What I have tried:

1. Stack Overflow
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Posted 20-Nov-20 5:09am

whataweird

Updated 20-Nov-20 5:37am

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Comments

KarstenK 20-Nov-20 13:40pm

The compiler is already talking to you: "Where is that comparator?". It like your "better half" demanding to clean up the kitchen ;-)

2 solutions

Solution 1

The sort function does not know how to sort a StudentDataTypes structure. You must provide a comparator, see <algorithm> functions | Microsoft Docs[^].

Posted 20-Nov-20 5:35am

Richard MacCutchan

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This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

k5054 · Accepted Answer · 2020-11-20T05:37:00

You need to tell sort how to compare the two structs. since there's no default comparison for non basic types. Do you want to sort by name or by grade, or by grade then by name, or ...?

Probably the easiest way is to add an operator< method to the struct:

C++

struct StudentDataTypes
{
    std::string name{};
    int grade{};
    // order by name:
    bool operator<(const struct StudentDataTypes& other) const 
    {
        return name < other.name;
    }
};

see further details here: std::sort - cppreference.com[^]

How do I solve this std::sort and struct issue?

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Solution 1

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How do I solve this std::sort and struct issue?

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