CODEWITHSUNDEEP
cmergesegmentation-fault
Buck925
Buck925

Reputation: 43

seg fault merge sort porgram

Im getting a seg fault in my code at line 44 with my fscanf function and i was hoping someone can tell my why it is not happy with this, thanks in advance for any help. I've ran it through gdb and when i went through line by line it trips up at the fscanf in my main.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <errno.h>   // for errno
#include <limits.h>  // for INT_MAX

void mergeSort(int a[], int low, int high);
void merge(int a[], int low, int mid, int high);

int main(int argc, char** argv)
{
    if(argc != 3){
      printf("Incorrect number of arguments\n");
      printf("Please enter a.out, # of numbers, and input file\n");
      return 1;
   }

   FILE* fp = fopen(argv[2], "r");

   char *p;
   int num;
   errno = 0;

   int conv = strtol(argv[1], &p, 10);

   // Check for errors: e.g., the string does not represent an integer
   // or the integer is larger than int
   if (errno != 0 || *p != '\0' || conv > INT_MAX) {
        // Put here the handling of the error, like exiting the program with
        // an error message
    } 
    else {
    // No error
    num = conv;
    }

   int i, k = 0;

   int array1[num];

   while(!feof(fp))
   {
        fscanf(fp, "%d", &array1[i]); //SEG FAULT HERE
        i++;
   }

   mergeSort(array1, 0, num);

   for(k = 0; k < num; k++)
   {
        printf("%d\n", array1[k]);
   }

   return 0;
}

void merge(int a[], int low, int mid, int high)
{
    int b[10000];
    int i = low, j = mid + 1, k = 0;

    while (i <= mid && j <= high) {
        if (a[i] <= a[j])
            b[k++] = a[i++];
        else
            b[k++] = a[j++];
    }
    while (i <= mid)
        b[k++] = a[i++];

    while (j <= high)
        b[k++] = a[j++];

    k--;
    while (k >= 0) {
        a[low + k] = b[k];
        k--;
    }
}

void mergeSort(int a[], int low, int high)
{
    if (low < high) {
        int m = (high + low)/2;
        mergeSort(a, low, m);
        mergeSort(a, m + 1, high);
        merge(a, low, m, high);
    }
}

Upvotes: 0

Views: 105

Answers (1)

Charlie Burns
Charlie Burns

Reputation: 7056

Your variable i is not initialized in the statement where the seg fault happens. 

   int i, k = 0;

   int array1[num];

   while(!feof(fp))
   {
        // i is not initliazed here
        fscanf(fp, "%d", &array1[i]); //SEG FAULT HERE
        i++;
   }

You probably want to initialize it to zero:

   int i = 0, k = 0;

Also, you really need to make sure num is initialized when this statement is executed:

   int array1[num];

Upvotes: 2

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