Common Mistakes in Pointers (C Language)

Pointers are powerful but tricky in C. Here are the most common mistakes beginners and even experienced C programmers make, along with explanations and how to avoid them.

❌ Uninitialized Pointer

int *ptr;  // uninitialized — points to random memory
*ptr = 42; // undefined behavior!

✅ Fix: Always initialize pointers before use.

int x = 42;
int *ptr = &x;

❌ Dereferencing a NULL Pointer

int *ptr = NULL;
printf("%d\n", *ptr);  // Crash: dereferencing NULL
✅ Fix: Check for NULL before dereferencing.

if (ptr != NULL) {
    printf("%d\n", *ptr);
}

❌ Double Free

free(ptr);
free(ptr);  // undefined behavior

✅ Fix: Set pointer to NULL after freeing.

free(ptr);
ptr = NULL;

❌ Pointer Arithmetic on Invalid Memory

int *ptr = malloc(5 * sizeof(int));
int *end = ptr + 10;  // out-of-bounds
✅ Fix: Never go beyond the allocated range.

❌ Returning Pointer to Local Variable

int *getPtr() {
    int x = 5;
    return &x;  // x is destroyed after return!
}
✅ Fix: Use malloc() to return persistent memory, or use static/global vars.

✅ Pro Tips