Why does a C program crash if a large variable is declared?

Question

I have the following C program compiled in Microsoft Visual Studio Express 2012:

int main() {
   int a[300000];
   return 0;
}

This crashes with a stack overflow in msvcr110d.dll!__crtFlsGetValue().

If I change the array size from 300,000 to 200,000 it works fine (in so much as this simple program can be said to 'work' since it doesn't do anything).

I'm running on Windows 7 and have also tried this with gcc under Cygwin and it produces the same behaviour (in this case a seg fault).

What the heck?

Answer 1

There are platform-specific limits on the size of the space used by automatic objects in C (the "stack size"). Objects that are larger than that size (which may be a few kilobytes on an embedded platform and a few megabytes on a desktop machine) cannot be declared as automatic objects. Make them static or dynamic instead.

In a similar vein, there are limits on the depth of function calls, and in particular on recursion.

Check your compiler and/or platform documentation for details on what the actual size is, and on how you might be able to change it. (E.g. on Linux check out ulimit.)