What's the difference between Viread in VC and VB？

In VB,the  "VISA32.DLL" Declare is

Declare Function viRead Lib "VISA32.DLL" Alias "#256" (ByVal vi As Integer, ByVal Buffer As String, ByVal count As Integer, ByRef retCount As Integer) As Integer

and use like 

viread（vi ,String,count ,retCount ）

In VC，

#include <visa.h>

and use like 

  viRead(vi, (UCHAR *)buf(), bufSize, &actual);

Buffer in VB is a String，but in VC is a  Integer array.

Why？