CODEWITHSUNDEEP
c++qsort
Slazer
Slazer

Reputation: 4990

Using the qsort from cstdlib

I am trying to run qsort from cstdlib. The function

qsort( m_all_animals , numberOfAnimals() , sizeof(Animal*) , compare);

executes successfully but it doesn't sort the m_all_animals. Actually, it does nothing to the array. The underlying data structures are here

Animal** m_all_animals;

//the number of elements, I tested it and it works
int numberOfAnimals(){
    int result=0;
    for (int i=0;i<m_size*2;++i){
        if (m_all_animals[i]==NULL)
            break;
        ++result;
    }
    return result;
}

int compare (const void* p1, const void* p2){
        return ((Animal*) p1)->get_size()-((Animal*) p2)->get_size();
}

I have the following inheritance hierarchy if it helps

Animal<-Bear
Bear<-brown_bear
brown_bear<-white_bear
Bear<-panda_bear
Animal<-snail

Upvotes: 1

Views: 221

Answers (3)

Dietmar K&#252;hl
Dietmar K&#252;hl

Reputation: 153810

Don't use qsort() in C++! It is slow, not type-safe, and will wreck havoc when used on non-POD types. Use std::sort() instead.

Upvotes: 4

unxnut
unxnut

Reputation: 8839

Your pointers are not correct. You have an array of pointers (Animal *); it should be an array of Animal data type and not pointer if you want to use your compare. Or you will need to modify compare to work with Animal **.

Upvotes: 2

rodrigo
rodrigo

Reputation: 98348

Yours is an array of pointers to Animal, so your compare function actually takes pointers to pointers to Animal:

int compare (const void* p1, const void* p2){
        return (*(Animal**)p1)->get_size()-(*(Animal**)p2)->get_size();
}

Upvotes: 2

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