Why is it a good practice to initialize pointers?

Answer 1

A pointer is initialized by assigning the address of some object to it ...

int a; // an integer

int *pa; // a pointer

pa = &a; // initialize the pointer

(*pa); // use the pointer

... by allocating memoryand assigning that address to it ...

int *pa; // a pointer to an integer

pa = malloc (1 * sizeof(int)); // allocate

if (pa == NULL) {... exception processing ...}

(*pa); // use the pointer

... or by doing address computation with it ...

int a[10]; // an array of integers

int *pa; // a pointer to an integer

pa = &(a+3); // initialize to the fourth element

(*pa); // use the fourth element

Answer 2

Pointers should be initialized for the same reason that all variables should be initialized. If you don't initialize them before using them, your program's behavior is undefined. In the case of pointers, this is particularly true because a random pointer could easily point to something valid, but the wrong thing, and changing that wrong thing will cause all sorts of weird, hard-to-explain, behavior; and it will be difficult to track this down, because the point of real failure will not be the same as the point of detected failure.

My practice is to always initialize pointers to NULL at the point of definition, unless you can initialize them immediately. This way, accidentally using one results in a hard crash, usually memory access violation (0xC5 for windows) at location zero.

I would fire any programmer that repeatedly fails to initialize objects before use, and I would similarly flunk any student that does the same thing. It is that important.