Memory allocation question

Hi.

I was reading some articles about static and dynamic memory allocation and there is something I don`t understand.

As I read, in assembly is it possible to extend the space used on the stack by incrementing the stack pointer. So why in C every statically allocated variable must have its size explicitly defined when writing the program, and it cannot change during execution?

Let`s say, I need an array, but I don`t know its size from the beginning. In this case I have to declare a pointer, allocate memory for it on the heap with malloc() and as the array`s size grows, call realloc(). Why can`t I declare an array statically on the stack like int array[100] and if needed, change its size to 101 and push the next value on the stack?


I don`t have any experience in assembly, so please excuse me, if I said something stupid.

Thank you.

Quote:

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Originally Posted by raczzoli

So why in C every statically allocated variable must have its size explicitly defined when writing the program, and it cannot change during execution?

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You're confusing static storage duration with automatic storage duration here. It's true that objects with static storage duration may only be defined with a fixed size. Array objects with automatic storage duration, however, may be defined with a variable size on implementations that support variable length arrays.

Quote:

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Originally Posted by raczzoli

Why can`t I declare an array statically on the stack like int array[100] and if needed, change its size to 101 and push the next value on the stack?

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C doesn't have a stack.