Large array in GMP

Question

If I want to use large array say mpz_t A[100000], I got "Segmentation fault (core dumped)" during my compilation. Is there any easier way to solve this?

Answer 1

tpg2114's comment is spot on. Try:

/* at top */
#include <stdlib.h>

/* definition */
mpz_t *A;

/* initialization of A */
A = (mpz_t *) malloc(100000 * sizeof(mpz_t));
if (NULL == A) {
    printf("ERROR: Out of memory\n");
    return 1;
}

/* no longer need A */
free(A);

If the malloc call here triggers an error, you don't have enough memory available in your system.

If you're interested in using a static array on the stack, then you can try increasing the stack limit size in Linux with the ulimit command.

Answer 2

You might also consider using mpz_class in C++ (ref.) rather than mpz_t. It can make arbitrary precision arithmetic straightforward.

Here's a random example:

#include <gmp.h>
#include <gmpxx.h>
#include <iostream>
using namespace std;

int main() {
  mpz_class A[100000];
  for(int i=0;i<100000;i++) A[i]=142412+i;

  for(int i=0;i<100000;i++) cout << i << " " << A[i] << endl;

  return 0;
}

Compiled with e.g.:

g++ [[filename]] -lgmp -lgmpxx