Merge sort of characters in string C - c

Question

I have this working merge-sort algorithm in C. But it works only for integers. When I tried to change int to char, i'm getting segfault.
Can you please help me, what should I change in this code, so I could use MergeSort like this:
char*str = "test_string";
MergeSort(str, 0, strlen(str)-1);
void Merge(int *array, int left, int mid, int right){
int tempArray[right-left+1];
int pos=0,lpos = left,rpos = mid + 1;
while(lpos <= mid && rpos <= right){
if(array[lpos] <= array[rpos]){
tempArray[pos++] = array[lpos++];
}
else{
tempArray[pos++] = array[rpos++];
}
}
while(lpos <= mid) tempArray[pos++] = array[lpos++];
while(rpos <= right)tempArray[pos++] = array[rpos++];
int iter;
for(iter = 0;iter < pos; iter++){
array[iter+left] = tempArray[iter];
}
return;
}
void MergeSort(int *array, int left, int right){
int mid = (left+right)/2;
if(left<right){
MergeSort(array,left,mid);
MergeSort(array,mid+1,right);
Merge(array,left,mid,right);
}
return;
}
I'm lost. Thanks!

Answer 1

Change your declaration of array from int * to char * in both functions. Make tempArray a char[] instead of an int[]. You are trying to read memory that is 4x (or 8x) out of bounds at the end of the array, hence the seg-fault. Put another way, char is 1 byte (usually) while int is 4 or 8, so you are looking at items of a different size stacked next to each other. Also, do not pass in a const * for your string. Declaring a string as char*str = "test_string"; implies read-only memory on some systems. Use char str[] = "test_string"; instead. If you are not using strictly C, you can use C++ templates to make a function that works for int and char: http://www.codeproject.com/Articles/257589/An-Idiots-Guide-to-Cplusplus-Templates-Part-1

Answer 2

#include <stdio.h>
#include<ctype.h>
#include<string.h>
int Run_count=-1;
int main ( int argc , char *argv[] )
{
/* if you dont want to use argv, put the elements in A yourself,
size being the number of string*/
/*L --> left side, R --> right side*/
int i = 0;
int size = argc-1;
char *A[argc-1];
for(i=1;i<=argc;i++){*(A+i-1) = argv[i];}
Caller(A,size);
for(i=0;i<size;i++){
printf("%s\n", A[i]);
}
printf("%d",Run_count);
}
int Caller(char* A[] , int n){
Run_count++;
int sizeL, sizeR ,i;
char *L[n/2+1] , *R[n-n/2+1];
if (n < 2){return 1;}
sizeL = n/2;
sizeR = n - sizeL;
for(i=0;i<sizeL;i++) {L[i] = *(A+i);}
for(i=0;i<n - n/2;i++) {R[i] = *(A+i+n/2);}
Caller( L, sizeL);
Caller( R, sizeR);
merger( L,sizeL, R,sizeR, A);
}
void merger(char* L[], int lengthL , char* R[] , int lengthR , char *A[]){
int i, j, k ,t =0 ;
for(k = 0 , j = 0; k < lengthL && j < lengthR ;t++){
if(compare(*(L+k),*(R+j))){
*(A+t) = *(L+k);
k++;}
else{*(A+t) = *(R+j);j++;}
}
while(k < lengthL ){
*(A+t) = *(L+k);
k++;t++;
}
while(j < lengthR ){
*(A+t) = *(R+j);
j++;t++;}
}
int compare(char *line1 , char *line2 )
{
int i;
for(i = 0;*(line1 + i) != '\0' && *(line2 + i) != '\0' ;){
if(isdigit(*(line1+i)) && isalpha(*(line2+i))){return 0;}
else if(isdigit(*(line2+i)) && isalpha(*(line1+i))){return 1;}
else if(*(line1 + i) > *(line2 + i)){return 0;}
else if(*(line1 + i) == *(line2 + i)){i++;}
else{return 1;}
}
}