Sorting a vector of objects alphabetically in c++

Question

So I've created a vector which contains product objects. The product has a int ID, string manufacturer and string productname. Lets say I've stored a few products by doing this

vector<product*>productlist;
 Product*p = new Product(123, "Sony", "C vaio laptop")
 Product*p1 = new Product(1234, "LG", "D 54 inch TV")
 Product*p2 = new Product(1235, "Lays", "A potato chips")
productlist.push_back(p);
productlist.push_back(p1);
productlist.push_back(p2);

I have a method called getproductname(){return productname;} which can be used to get the productname, and I can sort the productnames, but after that I have no idea how to continue as I don't know how to print the whole object by alphabetically of their productname.

Now I want to sort/print the 3 products by alphabetical order of their productname. How can I do that(the sorting part)? Sample output:

Products sorted alphabetically

Product ID1: 1235

Product manufacturer: Lays

Product name:A potato chips //name starts with A so it's the first output

Product ID2: 123

Product manufacturer: Sony

Product name: C vaio laptop

Product ID3: 1234

Product manufacturer: LG

Product name: D 54 inch TV //name starts with D so it's the last

I've tried inserting sort(productlist.begin(), productlist.end()); but it only works on vectors with string and not objects.

question asked was too vague/simple at first. Edited!

Answer 1

The easiest way is to use std::sort() function from the standard library. You can try something like this:

#include <iostream>     // std::cout
#include <algorithm>    // std::sort
#include <vector>       // std::vector

bool compareFunction (std::string a, std::string b) {return a<b;} 
//compare any way you like, here I am using the default string comparison

int main () 
{
  std::string myNames[] = {"Henry","Tom","Jafar","Alice","Bob","Cindy","Clara","Michael"};

  std::vector<std::string> myvector (myNames, myNames+8); //create vector from array

  std::sort(myvector.begin(),myvector.end(),compareFunction);//sort the vector


  std::cout << "Sorted vector:";
  for (std::vector<std::string>::iterator it=myvector.begin(); it!=myvector.end(); ++it)
        std::cout << ' ' << *it;
  std::cout << '\n';

  return 0;
}

I would recommend you look into the documentation for more details on std::sort

Answer 2

The way to make sorting happen using STL containers is to define a comparator function that tells the std::sort algorithm how to compare the elements to place them in order. So we need to define a less than relationship which we can do by creating a less than operator for our Product class like this:

struct Product
{
    int ID = 0;
    std::string manuf;
    std::string name;

    Product(int ID, const std::string& manuf, const std::string& name)
    : ID(ID), manuf(manuf), name(name) // initialize members here
    {
    }

    // overloading the < operator enables functions
    // like std::sort to compare Product objects to
    // order them accordingly
    bool operator<(const Product& p) const
    {
        return name < p.name; // order by name
    }
};

Now if we send a container full of Product objects to std::sort they will be sorted according to name.

However, we need to sort Product objects through their pointers so we need another less than operator to hand to the std::sort function that dereferences the pointers before making the comparison using our comparator function.

// Function object to sort pointers
struct SortProductPointers
{
    // overload the function call operator
    bool operator()(const Product* lhs, const Product* rhs) const
    {
        // dereference the pointers to compare their targets
        // using the Product class's operator<(...) function
        return *lhs < *rhs;
    }
};

Now we have those two we can call our std::sort algorithm:

int main()
{
    std::vector<Product*> products;

    products.push_back(new Product(1, "Lays", "A potato chips"));
    products.push_back(new Product(3, "LG", "D 54 inch TV"));
    products.push_back(new Product(2, "Sony", "C vaio laptop"));

    // std::sort takes a third parameter which is the 
    // comparator function object    
    std::sort(products.begin(), products.end(), SortProductPointers());

    for(const auto* p: products)
        std::cout << p->ID << ": " << p->manuf << ", " << p->name << '\n';

    // Don't forget to delete all your Products
    for(auto* p: products)
        delete p;
}