关于VC写的DLL函数被VB6.0调用的问题

在vc写的DLL里面定义Getabc函数有两个参数（其中b是指针的返回参数）；

我用c#调用这个DLL的时候,通过 int aa=Getabc(a,ref *b); 这样可以获得函数返回值，以及判断后【b】的值；

但是用VB调用的时候，给*b赋值的时候出错；因为VB6 加了ByVal关键字后，VB会在字符串尾加上Null字符，即自动将VB字符串转换成C-style字符串，然后将指向该串的指针传给DLL。这样赋值的地址就有NULL字符，就出错了。。。

知道出错的原因，真心不知道该怎么修改，请各位高手不吝赐教，小弟先行谢过！！！！！
email: woshinide1983@163.com


VC里定义的函数：
--------------------------------------------
extern "C" __declspec(dllexport) int _stdcall Getabc(double a,double *b);
int _stdcall Getabc(double a,double *b);
{
if(a>100)
{
*b = 101;
return 1;
}else if( a < 100)
{
*b = 99;
return 0;
}else
{
*b = 100;
return 0;
}
}
--------------------------------------------
VB里面的调用
---------------------------------------------
Private Declare Function Getabc Lib "abc.dll" Alias "_Getabc@56" (ByVal a As Double, ByVal b As Long) As Integer

Private Sub Command1_Click()

Dim b As Long
Dim aa As Integer

aa = Getabc (99, ByVal b)
If aa > 0 Then
MsgBox ("aaaaa")
Else
if(b == 100)
{
MsgBox ("bbbbbbb")
}else
{
MsgBox ("ccccccc")
}
End If
End Sub
------------------------------





[最优解释]

'传地址用ByRef
Private Declare Function Getabc Lib "abc.dll" Alias "_Getabc@56" (ByVal a As Double, ByRef b As Double) As Integer
'或什么都不加，默认是ByRef的
'Private Declare Function Getabc Lib "abc.dll" Alias "_Getabc@56" (ByVal a As Double, b As Double) As Integer

Private Sub Command1_Click()

      Dim b As Double
      Dim aa As Integer

      aa = Getabc (99, ByVal b)
    If aa > 0 Then
        MsgBox ("aaaaa")
    Else
        if(b == 100) 
 
        {
             MsgBox ("bbbbbbb")
        }else
        {
            MsgBox ("ccccccc")
        }
    End If
End Sub

[其他解释]

引用:

Visual Basic code?123456789101112131415161718192021222324'传地址用ByRefPrivate Declare Function Getabc Lib "abc.dll" Alias "_Getabc@56" (ByVal a As Double, ByRef b As Double) As Integer'或什么都不……

aa = Getabc (99, b)
[其他解释]

引用:

引用:
Visual Basic code?123456789101112131415161718192021222324'传地址用ByRefPrivate Declare Function Getabc Lib "abc.dll" Alias "_Getabc@56" (ByVal a As Double, ByRef b As Double) As Integer……

我也是这样写的，但是还是不对的，原因就是因为在C里面接受到的地址多了一个NULL空字符，所以没法再C里面给这个地址赋值，看图