Question

I am writing a counting sort function and when I run it, a window pops up saying “filename.exe has stopped working”. After debugging it looks like it is getting stuck in the second for loop. What really confuses me, is if I set maxInt to any number greater than 130000 it works, but if its 130000 or lower than I get that error message. The file I’m using to sort only has about 20 numbers.

#include <iterator>
#include <algorithm>
#include <vector>
#include <fstream>
#include <iostream>
using namespace std;

std::string file = "";
std::vector<int> numbers;

void CountingSort(vector<int> &numbers);

int main()
{
    std::cout << "Which file would you like to sort?\n";
    std::cin >> file;

    std::ifstream in(file.c_str());

    // Read all the ints from in:
    std::copy(std::istream_iterator<int>(in), std::istream_iterator<int>(),
            std::back_inserter(numbers));

    CountingSort(numbers);

    // Print the vector with tab separators:
    std::copy(numbers.begin(), numbers.end(),
            std::ostream_iterator<int>(std::cout, "\t"));
    std::cout << std::endl;

    return 0;
}

struct CalcMaxInt
{
    int maxInt;
    CalcMaxInt () : maxInt(0) {}
    void operator () (int i) { if (i > maxInt) maxInt = i; }
};

void CountingSort(vector<int>& numbers)
{
    CalcMaxInt cmi = std::for_each(numbers.begin(), numbers.end(), CalcMaxInt());
    //int maxInt = cmi.maxInt + 1;
    int maxInt = 130001;

    vector <int> temp1(maxInt);
    vector <int> temp2(maxInt);

    for (int i = 0; i < numbers.size(); i++)
    {
        temp2[numbers[i]] = temp2[numbers[i]] + 1;
    }

    for (int i = 1; i <= maxInt; i++)
    {
        temp2[i] = temp2[i] + temp2[i - 1];
    }

    for (int i = numbers.size() - 1; i >= 0; i--)
    {
        temp1[temp2[numbers[i]] - 1] = numbers[i];
        temp2[numbers[i]] = temp2[numbers[i]] -1;
    }

    for (int i =0;i<numbers.size();i++)
    {
        numbers[i]=temp1[i];
    }
    return;
}

Answer 1

You are trying to access an element out of proper range.
temp2 has range [0…maxInt-1] but the following code uses temp2[maxInt] which is out of range.

for (int i = 1; i <= maxInt; i++)
{
    temp2[i] = temp2[i] + temp2[i - 1];
}

You’ll have to fix temp2 to have maxInt+1 elements or i < maxInt to not to see the error.