c - qsort() giving random results -

in above program, create array of pointers char using malloc , attempt sort "strings" using qsort. i'm getting incorrect results. more importantly, i'm getting different results every time run program.

#include <stdio.h> #include <stdlib.h> #include <string.h> #define maxline 1000  #define maxchars 1000  int ballin_compare(const void *, const void *);   int main(int argc, char *argv[]){     char *linebuffer, **pointbuffer;      file *fp;         int = 0;            if(argc < 2 || (fp = fopen(argv[1], "r")) == null)             return 1;       linebuffer = (char *)malloc(maxchars);      pointbuffer = (char **)malloc(sizeof(char *) * maxline);       while(i < maxline && fgets(linebuffer, maxchars, fp) != null){         pointbuffer[i] = (char *)malloc(strlen(linebuffer));          strcpy(pointbuffer[i++], linebuffer);      }      free(linebuffer);      qsort(pointbuffer, i, sizeof(char *), ballin_compare);       fclose(fp);      if((fp = fopen(argv[1], "w")) == null)         return 1;       int x;      for(x = 0; x < i; x++)         fputs(pointbuffer[x], fp);      fclose(fp);      printf("%s sorted successfully", argv[1]);         return 0;    }    int ballin_compare(const void *c, const void *d){     char *a = (char *)c;      char *b = (char *)d;       int = 0;     while(a[i] && b[i] && a[i] == b[i])         i++;       if(a[i] < b[i])        return -1;      if(a[i] > b[i])        return 1;       return 0;  } 

my guess messed strcmp equivalent. ideas comparisons went wrong?

the problem qsort passes in pointers elements of array. since array elements of type char *, comparison function receives char ** inputs. written, comparing addresses if strings, naturally results in nonsense results.

you should write

const char *a = *(const char **)c; const char *b = *(const char **)d; 

in ballin_compare.