How to qsort an array of pointers to char in C?

Question

Suppose I have an array of pointers to char in C:

char *data[5] = { "boda", "cydo", "washington", "dc", "obama" };

And I wish to sort this array using qsort:

qsort(data, 5, sizeof(char *), compare_function);

I am unable to come up with the compare function. For some reason this doesn't work:

int compare_function(const void *name1, const void *name2)
{
    const char *name1_ = (const char *)name1;
    const char *name2_ = (const char *)name2;
    return strcmp(name1_, name2_);
}

I did a lot of searching and found that I had to use ** inside of qsort:

int compare_function(const void *name1, const void *name2)
{
    const char *name1_ = *(const char **)name1;
    const char *name2_ = *(const char **)name2;
    return strcmp(name1_, name2_);
}

And this works.

Can anyone explain the use of *(const char **)name1 in this function? I don't understand it at all. Why the double pointer? Why didn't my original function work?

Thanks, Boda Cydo.

Answer 1

@bodacydo here is a program that may explain what other programmers are trying to convey but this would be in context of "integers"

#include <stdio.h>


int main()
{
    int i , j;
    int *x[2] = {&i, &j};

    i = 10; j = 20;

    printf("in main() address of i = %p, address of j = %p \r\n", &i, &j);

    fun(x);
    fun(x + 1);

    return 0;
}


void fun(int **ptr)
{
    printf("value(it would be an address) of decayed element received = %p, double dereferenced value is %d \r\n",*ptr, **ptr);
    printf("the decayed value can also be printed as *(int **)ptr = %p \r\n", *(int **)ptr );
}