struct - sorting a c-string with qsort

Question

I'm sorting a bunch of IPs, but for some reason they come in the wrong order. I'm not quite sure where could be the problem.

66.249.71.3      
190.148.164.245  
207.46.232.182   
190.148.164.245  
190.148.164.245  
202.154.114.253
190.148.164.245  
190.148.164.245  
66.249.71.3      
190.148.164.245  
202.154.114.253

Here it is the way Im sorting them.

typedef struct {
    char *ip;
} mystruct;

/* qsort */
int struct_cmp(const void *a, const void *b)
{
    mystruct *ia = (mystruct *)a;
    mystruct *ib = (mystruct *)b;
    return strcmp(ia->ip, ib->ip);
} 
...
qsort(a_struct, 11, sizeof(mystruct*), struct_cmp);
for(..){
    printf("%s\n",a_struct[i]->ip);
}

Any help will be appreciate it. Thanks

Answer 1

You have an array of pointers to mystructs, but qsort with this comparision function would expect a simple array of mystructs. To sort an array of mystruct* you need to add another level of indirection to the comparison function:

int struct_cmp(const void *a, const void *b) {
    mystruct *ia = *(mystruct **)a;
    mystruct *ib = *(mystruct **)b;
    return strcmp(ia->ip, ib->ip);
}