Question

While solving a DP related problem, I observed that first works but the second seg faults .
What is the actual reason and what is the memory limit for just using int ?

int main(){
    static int a[3160][3160];
    return 0;
}

int main(){
    int a[3160][3160];
    return 0;
}

Answer 1

Because you probably don’t have enough stack memory to store that big array.

Second Example creates an array on stack, while the First example creates an array which is not located on stack but somewhere in the data/Bss segment, since you explicitly specify the storage criteria using static qualifier.

Note that c++ standard does not specify stack or heap or data segment or Bss segment these are all implementation defined details. The standard only specify’s behavior expected of variables declared with different storage criteria. So, where the variables are actually created is implementation defined but one thing for sure is, both your examples will create the arrays in different memory regions and the second one crashes because there is not enough memory in that region.

Also, probably if you are creating an array of such huge dimensions in actual implementation your design seems flawed and you might want to consider revisiting it.

You might also want to consider using std::array or std::vector, instead of the traditional c-style arrays.