How to compare C++ string using qsort in c?

Question

I tried to learn the qsort function of the c-library stdlib. This is provided even in c++. But i dont understand how to use them for sorting

Answer 1

Your error is in the declaration of the size in qsort. What is expected is the size of a member, which is, in your case, a string. So you want to use:

qsort(obj, 4, sizeof(string), compare_str);

However, you need to work with pointer to string, rather than strings themselves. Then, the code should look like:

int compare_str( const void *a, const void *b){
   const string*  obj = (const string*)a;
   const string* obj1 = (const string*)b;
   return obj->compare(*obj1);
}

// ...

string* obj[4] = { new string("fine"), new string("ppoq"),
                   new string("tri"), new string("get") };
qsort(obj, 4, sizeof(string*), compare_str);
// And delete the objects
for(int i = 0 ; i < 4 ; ++i) delete obj[i];