C Programming·The fundamentals of memory

Dynamic memory

malloc reserves memory; free returns it. Every path must agree.

Beginner 15 min read Lesson 9 of 300 Challenge included

What you will be able to do

Check malloc for NULL before using the result.
Free exactly once; set the pointer to NULL after freeing when it may be reused.
Compile with -fsanitize=address during development.

In plain English

Dynamic memory is needed when the size is unknown at compile time. Check every allocation, avoid use-after-free, and make ownership explicit. AddressSanitizer turns many invisible memory bugs into actionable reports.

array.cC

#include <stdio.h>
#include <stdlib.h>

int main(void) {
    size_t length = 3;
    int *scores = malloc(length * sizeof(int));
    if (scores == NULL) {
        return 1;
    }

    scores[0] = 8;
    scores[1] = 9;
    scores[2] = 7;
    printf("%d\n", scores[1]);

    free(scores);
    scores = NULL;
    return 0;
}

Your turn

Allocate and free a score array

Medium

Allocate an array of five ints, check the allocation, write one value and free it.

C · starter

int *scores = NULL;

Check your understanding before moving on.

Knowledge checkQuestion 1

What is use-after-free?

Select an answer to continue

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