advanced patterns when using qsort with custom comparator for struct array in C
I'm working on a personal project and I keep running into I'm a bit lost with I've searched everywhere and can't find a clear answer... Does anyone know how to I tried several approaches but none seem to work. I'm working with an scenario while trying to sort an array of structs using the `qsort` function in C. My struct contains several fields, and I wrote a custom comparator function to sort based on one of the fields. However, after sorting, the order of some elements seems incorrect, and I'm not sure why. Here’s what I have: ```c #include <stdio.h> #include <stdlib.h> typedef struct { int id; float value; } Item; int compare(const void *a, const void *b) { Item *item1 = (Item *)a; Item *item2 = (Item *)b; return (item1->value > item2->value) - (item1->value < item2->value); } int main() { Item items[] = {{1, 3.5}, {2, 2.1}, {3, 4.4}, {4, 2.1}}; int n = sizeof(items) / sizeof(items[0]); qsort(items, n, sizeof(Item), compare); for (int i = 0; i < n; i++) { printf("ID: %d, Value: %.2f\n", items[i].id, items[i].value); } return 0; } ``` In this example, I expect `items` to be sorted in ascending order based on the `value` field. However, I'm noticing that the items with the same `value` (like the two items with value `2.1`) are not maintaining their original relative order after the sort. I thought `qsort` was supposed to be stable for equal elements? Am I misunderstanding the behavior of `qsort`? Or is there something wrong with my comparator function? I've also tried changing the comparator to return `0` for equal values instead of using the subtraction method, but that also didn’t help. I'm using GCC version 11.2.0 on a Linux machine. Any insights or suggestions would be appreciated! This is part of a larger service I'm building. Thanks in advance! I appreciate any insights! For context: I'm using C on macOS. Is there a simpler solution I'm overlooking? I'm working with C in a Docker container on macOS. What am I doing wrong? What's the correct way to implement this?