Question

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Max Array Size in C

My question is: Does Code::blocks have a max number of iterations for a loop?

I am running a monte carlo and I would like to run a million particles through a for loop. But the max it seems to go without crashing is 110000.

Thanks!

Some more info:

I am using a random number generator seeded by time:

    srand(time(NULL));

I then want to create a million particles (random)

    for(k=0; k<M; k++){
    R[k] = rand()*(1)/(double)RAND_MAX;
    z[k] = -log(1 - R[k])/(1000*U);

where M = Num/10 (I want to #define N 1000000)

This is the only thing I can think of that is creating the problem?

Here is an example code that will not work.

    #include <stdio.h>
    #include <math.h>
    #include <time.h>
    #include <stdlib.h>

    int main(){

      srand(time(NULL));

       int j=0;
       int i;
       double A[1000000];

       for(i=0;i<1000000;i++){
          A[i] = rand()*(1.0)/(double)RAND_MAX;
           if (A[i] == 1.0){
              printf("Wow!\n");
           }
       }

       return 0;

    }

Could this be due to my settings of Code::blocks by any chance?

Answer 1

Edit: this is because the default maximum stack size is 1MB on Windows (but 8MB on Linux).

I don’t have a final answer, but I do know:

a) It runs fine from a Linux command-line.

b) Valgrind gives tons of errors of this form:

==2465== Invalid write of size 8
==2465==    at 0x804851D: main (test2.c:16)
==2465==  Address 0xbe4480e4 is on thread 1's stack
==2465== 
==2465== Invalid write of size 4
==2465==    at 0x8048521: main (test2.c:16)
==2465==  Address 0xbe4480e0 is on thread 1's stack
==2465== 
==2465== Invalid read of size 4
==2465==    at 0x4081D69: printf (printf.c:35)
==2465==    by 0x8048528: main (test2.c:16)
==2465==  Address 0xbe4480e0 is on thread 1's stack
==2465== 
==2465== Invalid read of size 8
==2465==    at 0x407AC05: vfprintf (vfprintf.c:1622)
==2465==    by 0x4081D7F: printf (printf.c:35)
==2465==    by 0x8048528: main (test2.c:16)
==2465==  Address 0xbe4480e4 is on thread 1's stack

c) The errors are clearly related to reading and writing from the array. This simpler version of the program does not cause any Valgrind errors:

#include <stdio.h>
#include <math.h>
#include <time.h>
#include <stdlib.h>

int main(){
  srand(time(NULL));
  int i;
  for(i=0;i<1000000;i++){
     if (rand()*(1.0)/(double)RAND_MAX == 1.0){
         printf("Wow!\n");
     }
  }
  return 0;
}