What is a memory leak in C and how to avoid it?

A memory leak happens when the program allocates memory with malloc(), calloc() or realloc() but never frees it. The program keeps using more and more memory, and a long running program can finally crash.

void leak(void) {
    int *p = malloc(100 * sizeof(int));
    // no free(p) here, and the pointer p is lost when the function ends
}

How to avoid it:

• Call free() for every malloc().
• Free the memory on all paths, also on the error paths.
• Set the pointer to NULL after freeing.
• Use tools like Valgrind or the AddressSanitizer (-fsanitize=address) to find leaks.

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