C++ sorting vector strings not working

Question

For some reason I cannot get this sort the names correctly. Can anyone tell me what is wrong with it? As far as I can tell the problem is that the strings are not compared correctly. I have tried string comparisons before, and I know this kind of code should work. It really has me stumped.

#include <iostream>
#include <fstream>
#include <string>
#include <vector>

using namespace std;

void sortNames(vector<string> &);

void main()
{
    vector<string> namesList;
    ifstream namesFile;
    namesFile.open("Names.txt");

    // Make sure the file exists.
    if (namesFile)
    {
        // Get the names from the file.
        string name;
        while (getline(namesFile, name))
            namesList.push_back(name);

        // Sort the imported names.
        sortNames(namesList);

        for (int i = 0; i < namesList.size(); i++)
            cout << namesList[i] << endl;
    }
    else
    {
        cout << "Data files are missing";
    }

    namesFile.close();
}

void sortNames(vector<string> &list)
{
    for (int i = 0; i < list.size(); i++)
    {
        // Find the lowest value after i.
        int lowIndex = i;
        for (int j = i + 1; j < list.size(); j++)
        {
            string name = list[i];
            string name2 = list[j];

            if (name > name2)
                lowIndex = j;
        }

        // Flip the elements if there was a value lower than i.
        if (i != lowIndex)
        {
            string temp = list[i];
            list[i] = list[lowIndex];
            list[lowIndex] = temp;
        }
    }
}

This is a learning exercise in a textbook to learn sorting and searching algorithms. — Emrys90
– Emrys90, Commented Mar 8, 2013 at 22:54

Sergey Kalinichenko · Accepted Answer · 2013-03-08 22:53:03Z

5

Here is the problem: this line

string name = list[i];

should be

string name = list[lowIndex];

Your current implementation compares the element at j not to the smallest string that you have found so far, but to the string at index i. That is incorrect, because it does not find the smallest remaining string: instead, it finds the last string in the vector that is smaller than the current element at index i, which is not what you want.

answered Mar 8, 2013 at 22:53

Sergey Kalinichenko

729k85 gold badges1.2k silver badges1.6k bronze badges

Sign up to request clarification or add additional context in comments.

Comments

EHuhtala · Accepted Answer · 2013-03-08 22:54:02Z

0

rather than string name = list[i];, you want string name = list[lowIndex];

answered Mar 8, 2013 at 22:54

EHuhtala

5873 silver badges8 bronze badges

Collectives™ on Stack Overflow

C++ sorting vector strings not working

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related