Are there any size limitations for C structures?

Question

Are there any size limitations for C structures?

Answer 1

From the C standard:

5.2.4.1 Translation limits

1 The implementation shall be able to translate and execute at least one program that contains at least one instance of every one of the following limits:

... — 65535 bytes in an object (in a hosted environment only)
... — 1023 members in a single structure or union
... — 63 levels of nested structure or union definitions in a single struct-declaration-list ... 13) Implementations should avoid imposing fixed translation limits whenever possible.

Other than that, the upper bound is SIZE_MAX (maximum value for size_t).

Answer 2

Since the sizeof operator yields a result of type size_t, the limit should be SIZE_MAX.

You can determine the value of SIZE_MAX like this:

#include <stdint.h>
#include <stdio.h>

int main (void) {
  printf("%zu", SIZE_MAX);
  return 0;
}

This is what the compiler should allow. What the runtime environment allows is another story.

Declaring a similarly sized object on the stack (locally) in practice will not work since the stack is probably much, much smaller than SIZE_MAX.

Having such an object globally might make the executable loader complain at program startup.