How to sort by Alphabetical in C++

Question

I've been trying to sort a vector of Employee's with a string data member called last name. I've tried several different ways, using the sort method of vector, trying to convert my vectors to list and using its sorting, I even tried using string compare and > operators as shown below:

    vector<Employee>sortE(vector<Employee>record)
{
    for (unsigned int i = 0; i < record.size() - 1; i++)
        if (record[i].getLastName() > record[i+1].getLastName())
            swap(record[i], record[i + 1]);
    return record;
}

I thought if I used the above method with the swap function, it would work. But maybe since swap is a string method and I'm doing it with Employees it won't swap properly? But I've also tried it with my own "swap" like below:

vector<Employee>sortE(vector<Employee>record)
{
    Employee temp;
    for (unsigned int i = 0; i < record.size() - 1; i++)
        if (record[i].getLastName() > record[i + 1].getLastName())
        {
            temp = record[i];
            record[i] = record[i + 1];
            record[i + 1] = temp;
        }

    return record;
}

Either way I can't seem to get it to work properly, any insight or help would be appreciated.

Answer 1

You could try using a lambda if using C++11 or newer (also, I don't know what your Employee class looks like, so I made a trivial one). Also, check here for online execution: http://cpp.sh/6574i

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

class Employee
{
public:
    Employee( const std::string& firstName, const std::string& lastName ) :
        _firstName( firstName ),
        _lastName( lastName )
    {}

    ~Employee()
    {}

    std::string FirstName() const
    { 
        return _firstName;
    }

    std::string LastName() const
    {
        return _lastName;   
    }

    std::string FullName() const
    {
        return _firstName + " " + _lastName;   
    }

private:
    std::string _firstName;
    std::string _lastName;
};

int main()
{
    Employee e1( "Suresh", "Joshi" );
    Employee e2( "Mats", "Sundin" );
    Employee e3( "Steve", "Nash" );
    std::vector< Employee > employees { e1, e2, e3 };

    std::sort(employees.begin(), employees.end(), 
        [](const Employee& lhs, const Employee& rhs) -> bool
        { 
             return rhs.LastName() > lhs.LastName(); 
        });

    for ( auto employee : employees )
    {
        std::cout << employee.FullName() << std::endl;
    }
}

Answer 2

You can provide a lambda to std::sort :

std::vector<Employee> ve;
using std::begin;
using std::end;
std::sort(begin(ve), end(ve),
          [](const Employee& lhs, const Employee& rhs)
          {
              return lhs.getLastName() < rhs.getLastName();
          });

That said, in real life last names are not necessarily unique, and when they compare equal it's a good idea to fall back on first name, and if that's also equal some other field like an employee id:

              return lhs.getLastName() < rhs.getLastName() ||
                     lhs.getLastName() == rhs.getLastName() &&
                     (lhs.getFirstName() < rhs.getFirstName() ||
                      lhs.getFirstName() == rhs.getFirstName() &&
                      lhs.getId() == rhs.getId());