Question

On Linux, using C, assume I have an dynamically determined n naming the number of elements I have to store in an array (int my_array[n]) just for a short period of time, say, one function call, whereby the called function only uses little memory (some hundred bytes).

Mostly n is little, some tenths. But sometimes n may be big, as much as 1000 or 1’000’000.

How do I calculate, whether my stack can hold n*o + p bytes without overflowing?

Basically: How much bytes are there left on my stack?

Answer 1

Indeed, the checking available stack question gives good answer.

But a more pragmatic answer is: don’t allocate big data on the call stack.

In your case, you could handle differently the case when n<100 (and then allocating on the stack, perhaps thru alloca, makes sense) and the case when n>=100 (then, allocate on the heap with malloc (or calloc) and don’t forget to free it). Make the threshold 100 a #define-d constant.

A typical call frame on the call stack should be, on current laptops or desktops, a few kilobytes at most (and preferably less if you have recursion or threads). The total stack space is ordinarily at most a few megabytes (and sometimes much less: inside the kernel, stacks are typically 4Kbytes each!).