CODEWITHSUNDEEP
c++c
user2812045
user2812045

Reputation:

C++ still get segmentation fault (core dumped) error after change stack size with setrlimit

I wrote a C++ program in Ubuntu. In main function, I have 2-D array like this:

int main() {
   unsigned long long int s[11000][100];
   // some code to manipulate with s (just for initialization)
   // ...
}

And the program failed to run. After search the web, I know that the size of 2-D array exceeds the default stack size in Ubuntu which is about 8 MB. I tried some suggests to change stack size automatically in my program. So I added some few lines of code:

int main() {
   unsigned long long int s[11000][100];
   const rlim_t kStackSize = 32 * 1024 * 1024;
   struct rlimit rl;
   int result;

   result = getrlimit(RLIMIT_STACK, &rl);
   if (result == 0) {
      if (rl.rlim_cur < kStackSize) {
         rl.rlim_cur = kStackSize;
         result = setrlimit(RLIMIT_STACK, &rl);
         if (result != 0) {
            printf("error\n");
         }
   } else {
        printf("error\n");
   }

   // some code to manipulate with s (just for initialization)
   // ...
} // end main

But I still got the segmentation fault (core dumped) error. I also checked the stack size, its size is now 32 MB, 4 times lager than the size of 2-D array. Also try set stack size to RLIM_INFINITY, but failed again. Can anybody help me figure out the reason and the solution? Thank you so much!

Upvotes: 2

Views: 753

Answers (2)

greyfade
greyfade

Reputation: 25647

Given the size of this block of memory, you should instead allocate it with either new[] or malloc and delete[] or free it as appropriate. Or, if you're using C++, you should use std::vector or some other heap-allocated container.

The reason it is still crashing is because it's still trying to allocate more than some limit on the still-limited stack space, before you even try to adjust it. Variables in automatic storage (that is, on the stack) are allocated before the function executes.

Upvotes: 5

nitish712
nitish712

Reputation: 19764

One solution to overcome these type of problems is:

Always declare large arrays globally.

This avoids the problems such as yours since the memory for global variables is allocated in the Initialized Data Segment. For more information see this. Hope this helps.

Upvotes: 2

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