C char qsort in array of pointers to strings

Question

I have an array of pointers to string:

char *TAB[3] = { "dafafa", "alfkasf", "bafgr" };

I would like to sort characters in in each of those strings.

My compare function:

int cmp(const void *a, const void *b)
{
   return *(char *)a - *(char *)b; 
}

and while trying qsort on one of these:

qsort(TAB[0], 6, sizeof(char), cmp);

The program doesn't work. After many efforts I found that the reason of the problem is in delivering TAB[0] to qsort().

Can anyone explain why it doesn't work and how to fix that?

Answer 1

If you want to sort characters inside each string, the first thing you must ensure is that your strings can be written to. As it currently stands, your strings are read-only, so you cannot sort their characters without copying their content into memory that allows writing.

Next thing is that you need a loop. Since you are sorting each string individually, you need to loop through the array, and call qsort on each item. The initial item is TAB[i], and the length is strlen(TAB[i]). Your cmp function will work.