QSORT在C中的数组上？

Question

If I have an array like this:

2, 4, 6, 0, 0, 0, 0, 0, 0

1. Is there a way I can use qsort by sorting just the first 3 elements, and leaving the rest untouched?
2. Would qsort(arrNumbers, 3, sizeof(int), compare) do the job?
3. Does specifying the number of elements lower than the full array cause only that number of elements to become sorted?

EDIT: My compare function is:

int comp(const int * a, const int * b)
   if(a==b)
   {
       return 0;
   }
   else
   {
      if(a<b)
      {
         return -1;
       }
       else
       {
         return 1;
       }
    }

Does it seem right?

Answer 1

Yes.

Yes. ^*

Yes.

---

_{* Assuming you define compare() appropriately.}

Answer 2

Why don't you try it and see that it works as you expect?

Explanation: the qsort function only gets a pointer to the array, which does not say how long the array is. That's why you have to pass the size as well. In your function call you claim that the array is three int s long, and that's all the qsort function can be sure of. It will not access anything beyond that limit.

Answer 3

The full signature is:

void qsort(
   void * base,
   size_t num,
   size_t width,
   int (__cdecl *compare )(const void *, const void *) 
);

To sort a specific contiguous range of the array, you just pass in a different base (pointer to starting element for the range) and num (number of elements in the range).

Answer 4

是的，如果您指定3，则只会对前3个元素进行排序。