Visual Basic和Visual C++互动(标准DLL)

原文见Nicholas Skapura得 Interfacing VB and C++
VC++ DLL
1)DLL中的函数声明

void __declspec(dllexport) CALLBACK TestFunc()
{
	cout << "Inside the DLL!";
}

2）定义DEF文件

LIBRARY "testDLL_Library"
DESCRIPTION "An example DLL for interfacing with C++"

EXPORTS
	TestFunc  @1

VC++客户端调用TestFunc的代码
1）先声明
typedef int (WINAPI*ifunc)(int t);
ifunc RetInt;
2）通过LoadLibrary和GetProcAddress获得函数指针。
HINSTANCE hLib = LoadLibrary("testdll_library.dll");
if(hLib == NULL)
{
	cout << "ERROR: Unable to load library!" << endl;
	getch();
	return;
}
RetInt = (ifunc)GetProcAddress((HMODULE)hLib,"RetInt");
3）调用DLL中的函数。
if（RetInt !=NULL）
	RetInt();
else
	。。。
4）释放DLL
FreeLibrary((HMODULE)hLib);

VB客户端调用TestFunc的代码
1）声明
Declare Function RetInt Lib "../testdll_library.dll" (ByVal t As Integer) As Integer
2）调用
	call RetInt(1)

详细内容见<a href="http://www.flipcode.com/articles/article_vbdlls.shtml">Interfacing Visual Basic And C++</a>

其他
1）如果VB需要传递数组参数。那么VC DLL需要按照下面的方式完成

short __declspec(dllexport) CALLBACK ArrayExample(LPSAFEARRAY FAR *ArrayData)
{
	short *temp;
	temp = (short*)(*ArrayData)->pvData;
	return(temp[0]);
}
2）参数包含字符串
BSTR __declspec(dllexport) CALLBACK StringExample(BSTR stringVar)
{
	LPSTR buffer;
	buffer = (LPSTR)stringVar;
	::MessageBox(NULL,buffer,"in C++",0);
	buffer = _strrev(buffer);
	return(SysAllocString(stringVar));
}
3）返回字符串。需要通过调用SysAllocString事先分配空间给字符串。
return(SysAllocString(tempArray[index]));
4）回调函数
//VC++ DLL
// In C++
void __declspec(dllexport) CALLBACK CallbackExample(long Addr1)
{
	typedef void (__stdcall *FNPTR)(BSTR stringVar);
	FNPTR FunctionCall;
	LPSTR buffer = "hello!";
	FunctionCall = (FNPTR)Addr1;
	BSTR temp;
	temp = ChartoBSTR("hello");
	FunctionCall(SysAllocString(temp));
}
VB客户端
Declare Sub CallbackExample Lib "../testdll_library.dll" (ByVal Addr As Long)

Public Sub voidFunc(ByVal stringVar As String)
    MsgBox stringVar
End Sub