CODEWITHSUNDEEP
csegmentation-fault
Abhinav Gupta
Abhinav Gupta

Reputation: 13

SIGSEGV error keeps showing up

this error keeps on appearing for every program i try to submit on spoj.pl

In the given code i need to find prime numbers between m - n for t no. of test cases . problem statement:http://www.spoj.com/problems/PRIME1/ the same error is appearing .. can anyone plss tell me why this error shows up again nd again .. here's my code

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

int main()

{
  int t;
  scanf("%d",&t);
  int *m,*n;
  m=(int *)malloc(sizeof(int)*t);
  n=(int *)malloc(sizeof(int)*t);
  int i=0;
  while(i<t)
     {
          scanf("%d%d",(m+i),(n+i));
          i++;
      }
  i=0;
  while(i<t)
    {
      long long int *list,j,k;
      list=((long long int*)malloc(sizeof(long long int)*(n[i]+1)));
      list[0]=list[1]=0;
      for(j=2;j<=*(n+i);j++)
           {
               *(list+j)=1;
           }
      float l=sqrt(*(n+i)+1);
      //int l=sqrt(*(n+i)+1);

      for(j=2;j<=l;j++)
           {
               if(*(list+j)==1)
                   {
                       //printf("\n%ld",j);
                       for(k=j*j;k<=*(n+i);k=k+j)
                           *(list+k)=0;
                    }
            }
      for(j=m[i];j<=n[i];j++)
           {
               if(*(list+j)==1)
                   {
                       printf("\n%ld",j);
                    }
            }
      printf("\n");
      free(list);
      i++;
 }
free(m);
free(n);  
return 0;
}

Upvotes: 0

Views: 188

Answers (2)

K Scott Piel
K Scott Piel

Reputation: 4380

First -- you should not cast malloc -- it can cause unexpected errors.

Second, there's no validation that you allocated the memory you need. There are three different places you're asking for memory and never look to see if malloc returned a NULL result... if t and/or (n[i]+1) is sufficiently large, malloc() may be unable to get a chunk of memory big enough to satisfy the request, in which case you're trying to assign to a NULL pointer and you get a SIGSEGV -- there's a hint given in the description of the problem

Warning: large Input/Output data, be careful with certain languages (though most should be OK if the algorithm is well designed)

Upvotes: 2

Spam
Spam

Reputation: 637

Seems to work fine on my computer, except for the warning about using %ld (%lld should be used). I can only obtain a SIGSEGV error when putting 0 as a value for n[i]. Could you indicate what values you used to generate that error?

Edit : You are testing for the values "1 888888888 1000000000". Your computer simply can't allocate an array of such size. You are asking an array of size 1000000001 in your memory. That amounts to about 8GB (since a long long int as about 8B, at least on my computer), which is pretty much undoable for your computer.

Upvotes: 0

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