Sort an integer array with qsort.

C: The comparator uses relational comparisons to avoid subtraction overflow.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <stdint.h>
#include <stdbool.h>
#include <errno.h>
#include <limits.h>
#include <math.h>
#include <time.h>

static int compare_ints(const void *left, const void *right) {
    int a = *(const int *)left, b = *(const int *)right;
    return (a > b) - (a < b);
}
int main(void) {
    int values[] = {3,1,2};
    qsort(values,3,sizeof values[0],compare_ints);
    for (size_t i=0; i<3; i++) printf("%d\n",values[i]);
    return 0;
}

Expected output EXAMPLE

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3

Details

Save as snippet.c; compile with gcc -std=c17 -Wall -Wextra snippet.c -lm -o snippet, then run ./snippet. The comparator uses relational comparisons to avoid subtraction overflow.

✓ Verified

Tested on Ubuntu 24.04.5 LTS · 2026-11-02 18:02:30 UTC · gcc (Ubuntu 13.3.0-6ubuntu2~24.04.1) 13.3.0 · gcc 4:13.2.0-7ubuntu1

Test inputs, results and environment

The exact published code ran in a dedicated Linux test container with prepared inputs. Unprivileged snippet process, external networking disabled, read-only root filesystem, and a fresh temporary working directory. Fixtures and output records are isolated from the application database. Testing covers this example and its stated checks, not every input, operating system, or runtime version. The Linux container shares its host's kernel; this is not a native Windows test.

Architecture / host kernel: x86_64 / 6.18.54.1-microsoft-standard-WSL2
Snippet identity / locale: uid=65534, gid=65534 (unprivileged) / C.UTF-8
Interpreter invocation: gcc -std=c17 -Wall -Wextra -Werror snippet.c -lm -o snippet && ./snippet
Container image ID: sha256:32dc2d998158b6554c99b73b533f423696a0f3e31e8cbea9db10b5eee9a2fadd
Code SHA-256: 9a7a865d43afbb3783c4a71628478ed13002b38be6efbc41be9f5874dba66f66
Dependencies: gcc 4:13.2.0-7ubuntu1

Test input setup

These are the prepared inputs used by the test harness. See Details above for the prerequisites and how to run this example.

# No input files required.

Observed standard output

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Exit code: 0. Standard error: empty. Validation: Exact stdout comparison. System-dependent values above are one recorded run.

# C # Array transformations # sort