mergeSort.c

# include <stdio.h>
# include <stdlib.h> 
/* Function to merge the two haves arr[l..m] and arr[m+1..r] of array arr[] */
void merge(int *arr, int l, int m, int r)
{
    int i, j, k;
    int n1 = m - l + 1;
    int n2 =  r - m;
 
    /* create temp arrays */
    int L[n1], R[n2];
 
    /* Copy data to temp arrays L[] and R[] */
    for(i = 0; i < n1; i++)
        L[i] = arr[l + i];
    for(j = 0; j < n2; j++)
        R[j] = arr[m + 1+ j];
 
    /* Merge the temp arrays back into arr[l..r]*/
    i = 0;
    j = 0;
    k = l;
    while (i < n1 && j < n2)
    {
        if (L[i] <= R[j])
        {
            arr[k] = L[i];
            i++;
        }
        else
        {
            arr[k] = R[j];
            j++;
        }
        k++;
    }
 
    /* Copy the remaining elements of L[], if there are any */
    while (i < n1)
    {
        arr[k] = L[i];
        i++;
        k++;
    }
 
    /* Copy the remaining elements of R[], if there are any */
    while (j < n2)
    {
        arr[k] = R[j];
        j++;
        k++;
    }
}
 
/* l is for left index and r is right index of the sub-array
  of arr to be sorted */
void mergeSort(int *arr, int l, int r)
{
    if (l < r)
    {
        int m = l+(r-l)/2; //Same as (l+r)/2, but avoids overflow for large l and h
        mergeSort(arr, l, m);
        mergeSort(arr, m+1, r);
        merge(arr, l, m, r);
    }
}
 
 
/* UITLITY FUNCTIONS */
/* Function to print an array */
void printArray(int A[], int size)
{
    int i;
    for (i=0; i < size; i++)
        printf("%d ", A[i]);
    printf("\n");
}
 
/* Driver program to test above functions */
/*int main()
{
    int arr[] = {12, 11, 13, 5, 6, 7};
    int arr_size = sizeof(arr)/sizeof(arr[0]);
 
    printf("Given array is \n");
    printArray(arr, arr_size);
 
    mergeSort(arr, 0, arr_size - 1);
 
    printf("\nSorted array is \n");
    printArray(arr, arr_size);
    return 0;
}*/
int main(int argc, char *argv[])
{
	if(argc != 3)
	{
		printf("[*]Usage: merge_sort <Input File Name> <Number of elements>\n");
		return 0;
	}	
	int len = atoi(argv[2]), *arr, i;
	
	FILE *fp, *fw;
	fp = fopen(argv[1], "r");
	fw = fopen("sorted_file_merge.txt", "w");
	
	arr = (int *)malloc(len * sizeof(int));
	for(i = 0 ; i < len ; i++)
		fscanf(fp, "%d", &arr[i]);
	mergeSort(arr, 0, len - 1);
	for(i = 0 ; i < len ; i++)
		fprintf(fw, "%d\n", arr[i]);
	free(arr);
	
	fclose(fp);
	fclose(fw);
	return 0; 
}