In the middle of qsort, is there a way to stop it?

[hamidi]

qsort is an essential part of the standard C library in all platforms. In the compare function introduced to this function, I may conclude that two items are identical and I decide not to continue the process of sorting elements. How can I inform this to qsort not to continue sorting?

[SeppJ]

You can longjmp out of your comparison function.

Also, just post your spam link and be done, thanks.

[hamidi]

@SeppJ Oh no! It's dangerous. Thanks anyway.
What's spam link? I'm not a spammer!

[SeppJ]

For reference: https://stackoverflow.com/questions/79285431/in-the-middle-of-qsort-is-there-a-way-to-stop-it

[wob]

Since this was posted to the C++ section of the forum, I suggest std::sort + exceptions (the topic has been moved to C, so my answer is not really useful any more, but maybe still fun to play with)

#include <algorithm>
#include <fmt/core.h>
#include <fmt/ranges.h>
#include <vector>
#include <stdexcept>

using namespace std;

bool compare(int a, int b) {
    fmt::println("{} <=> {}?", a, b);
    if (a == b) throw runtime_error("Equal numbers compared");
    return a < b;
}

int main() {
    vector<int> a {1,5,3,5,6,2};
    try {
        sort(a.begin(), a.end(), compare);
    } catch (const runtime_error &e) {
        fmt::println("Stopped sorting: {}!", e.what());
    }
    fmt::print("A: {}!", a);
}