std::sort

[ghost1111]

my compiler doesnt like the way im doing std::vector and std::map for my sort is there any way to do it with just map

 std::vector< std::pair<std::string,student>> map;
	std::map<std::string, student>::const_iterator it;
	for(it = m_student.begin(); it != m_student.end(); it++)
    {
        map.push_back(*it);
    }
    std::sort(map.begin(),map.end(),[](std::pair<std::string,student> &a,std::pair<std::string,student> &b)
              {
                  return a.second < b.second;//i get and error here

              }

            );

[helios]

You can't sort an std::map. An std::map is always sorted according to its keys.
If you need the items in an std::map sorted by a different criterion then you need to copy them somewhere else (like onto a vector) and sort them there.

[ghost1111]

would you use copy() and how would you do that?

[helios]

Oops. My bad, I misread your code. I thought map was an std::map instead of an std::vector. You should avoid doing stuff like that.

std::map<int, int> string;
std::string pointer;

You should preferably name containers based on what data they contain; failing that, you should name them according to the type that they are, especially if the function is going to handle multiple containers.

return a.second < b.second;//i get and error here

Never say "an error". If you get an error then say what error you're getting. We can't look at your screen.

[ghost1111]

ok

[Enoizat]

This looks a question for clairvoyants: how to guess what’s wrong in a code without seeing the code and the error messages?

Hints:

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

struct Student { int id {}; };
void waitForEnter();

using Namestud = std::pair<std::string, Student>;

int main()
{
    std::vector<Namestud> map { { "Barbara", {2} }, { "Carol", {3} }, {"Ann", {1} } };
    std::sort(map.begin(), map.end(),
                [] (Namestud &a, Namestud& b) { return a.second.id < b.second.id; }
              );
    for(const auto& a : map) {
        std::cout << a.first << ' ' << a.second.id << '\n';
    }
    waitForEnter();
    return 0;   
}

void waitForEnter()
{
    std::cout << "\nPress ENTER to continue...\n";
    std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
}

Output:

Ann 1
Barbara 2
Carol 3

Press ENTER to continue...