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casting with strcmp sort function

Demonstrations of qsort which sort an array alphabetically usually define a sort function like this:

int compare(const void* A, const void* B) {
return( strcmp(*((char **)A), *((char **)B) ) );
}

Why is there a need to cast to char**, and then derefence to get a char* ? Why not just cast to char* ?

I tried:

int compare(const void* A, const void* B) {
return( strcmp((char *)A), (char *)B) ) );
}

This doesn't sort properly. But I can't see the difference between the two functions. Can someone explain why casting to char** and then dereferencing is functionally different than simply casting to char* ?

ASKER CERTIFIED SOLUTION

Infinity08

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Infinity08

It's easier if you make a drawing of the above example, showing the pointers etc.

Infinity08

And about that compare function, you'd have to call it like this :

int compare(const void* A, const void* B) {
return( strcmp(*((char **)A), *((char **)B) ) );
}

char *strA = "stringA";
char *strB = "stringB";
compare(&strA, &strB);

Is that how it's done ?

If you want to use your compare function, you'd call it like this :

int compare(const void* A, const void* B) {
return( strcmp((char *)A, (char *)B ) );
}

char *strA = "stringA";
char *strB = "stringB";
compare(strA, strB);

chsalvia

ASKER

>> And about that compare function, you'd have to call it like this :

Well, I wouldn't call it directly. It is just meant to be passed to qsort. I found the function in a qsort tutorial, in fact.

But I understand what you're saying about the different pointer locations. Thank you.