Question

While taking my first steps with C, I quickly noticed that int array[big number] causes my programs to crash when called inside a function. Not quite as quickly, I discovered that I can prevent this from happening by defining the array with global scope (outside the functions) or using malloc.

My question is:

Starting at which size is it necessary to use one of the above methods to make sure my programs won’t crash?

I mean, is it safe to use just, e.g., int i; for counters and int chars[256]; for small arrays or should I just use malloc for all local variables?

Answer 1

You should understand what the difference is between int chars[256] in a function and using malloc().

In short, the former places the entire array on the stack. The latter allocates the memory you requested from the heap. Generally speaking, the heap is much larger than the stack, but the size of each can be adjusted.

Another key difference is that a variable allocated on the stack will technically be gone after you return from the method. (Oh, your program may function as though it’s not gone for a bit if you continue to access that array, but ho ho ho danger lurks.) A hunk of memory allocated with malloc will remain allocated until you explicitly free it or the program exits.