How to Sort a 2D Array in C Using qsort()?

Sorting a 2D Array in C Using qsort()

When faced with the task of sorting a 2D array, one may consider utilizing built-in functions to simplify the process. In C , the qsort() function stands out as a powerful tool for this purpose. Unlike its counterpart, sort(), qsort excels in handling multiple-column sorting for fixed arrays.

The comparator function in qsort() takes a unique approach, utilizing a series of ternary statements to compare elements effectively. The result is an algorithm that adeptly handles sorting arrays based on specific column values.

Consider the following example, where a 2D array is populated with random data and requires sorting based on its first column:

<code class="cpp">#include <iostream>
#include <random>
#include <algorithm>

int main() {
    int ar[10][2];

    // Populate array with random data
    std::random_device rd;
    std::default_random_engine rng(rd());
    std::uniform_int_distribution<> dist(1, 20);
    std::for_each(std::begin(ar), std::end(ar), [&](int(&ar)[2]) { ar[0] = dist(rng); ar[1] = dist(rng); });

    // Sort the array
    std::qsort(ar, 10, sizeof(*ar),
        [](const void *arg1, const void *arg2) -> int {
            int const *lhs = static_cast<int const *>(arg1);
            int const *rhs = static_cast<int const *>(arg2);
            return (lhs[0] < rhs[0]) ? -1
                : ((rhs[0] < lhs[0]) ? 1
                : (lhs[1] < rhs[1] ? -1
                : ((rhs[1] < lhs[1] ? 1 : 0))));
        });

    // Display sorted array
    std::for_each(std::begin(ar), std::end(ar), [](const int(&ar)[2]) { std::cout << ar[0] << ',' << ar[1] << '\n'; });

    return 0;
}</code>

In this sample, the comparator ensures that the first column values are compared diligently to achieve the desired sorting. By leveraging qsort() and tailoring the comparator to suit your specific needs, you can efficiently sort 2D arrays in C , making data manipulation a breeze.

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