<stdlib.h> covers memory allocation (malloc, calloc, free), type conversion (atoi, strtol), sorting/searching (qsort, bsearch), and process control (exit, abort). It's the “junk drawer” of the C standard library.

Always check malloc for NULL; always check qsort comparators carefully for overflow.

This example sorts integers with qsort and binary-searches the result.

// compile: gcc -o stdlibexample stdlibexample.c
// run: ./stdlibexample
// description: sort array with qsort, then search it with bsearch
 
#include <stdlib.h>
#include <stdio.h>
 
int cmp_int(const void* a, const void* b) {
    return *(int*)a - *(int*)b;
}
 
int main() {
    int arr[] = {5, 2, 8, 1, 9, 3};
    int n = sizeof(arr) / sizeof(arr[0]);
 
    qsort(arr, n, sizeof(int), cmp_int);
 
    printf("sorted: ");
    for (int i = 0; i < n; i++) printf("%d ", arr[i]);
    printf("\n");
 
    int key = 8;
    int* found = bsearch(&key, arr, n, sizeof(int), cmp_int);
    printf("search for 8: %s\n", found ? "found" : "not found");
 
    return 0;
}