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/*
 * memory_demo.c — illustrates common memory errors and how
 * to detect them with Valgrind / AddressSanitizer.
 *
 * Compile clean (no errors):
 *   gcc -Wall -Wextra -std=c11 -g memory_demo.c -o memory_demo
 *
 * Check with Valgrind:
 *   valgrind --leak-check=full ./memory_demo
 *
 * Check with AddressSanitizer:
 *   gcc -fsanitize=address -g memory_demo.c -o memory_demo_asan
 *   ./memory_demo_asan
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(void)
{
    /* --- LEAK EXAMPLE (intentional for demo) --- */
    int *leaked = malloc(64 * sizeof(int));
    /* No free(leaked) — Valgrind will report this */

/* --- CORRECT allocation/free --- */
    char *msg = malloc(32);
    if (!msg) return EXIT_FAILURE;
    strncpy(msg, "Hello from heap", 31);
    msg[31] = '\0';
    printf("%s
", msg);
    free(msg);
    msg = NULL;   /* good habit: NULL after free */

/* --- DOUBLE-FREE (commented out — UB!) --- */
    /* free(msg);  <-- would be double-free since msg is now NULL (safe) */
    /* free(leaked); free(leaked);  <-- actual double-free */

/* --- USE-AFTER-FREE (commented out — UB!) --- */
    /* free(leaked);  printf("%d
", leaked[0]);  <-- UB */

/* Clean up the leaked pointer so the demo actually runs clean */
    free(leaked);

printf("Done. Run under valgrind for memory analysis.
");
    return EXIT_SUCCESS;
}