DLL动态调用碰倒有关问题！各位大侠，帮忙看看呀！

DLL动态调用碰倒问题！各位大侠，帮忙看看呀！！
贴一下代码：
[code=C/C++][/code]
[code=C/C++][/code]
void __fastcall TForm1::Button1Click(TObject *Sender)
{
  int i=0;
  hInst = LoadLibrary("Project1.dll");
  if(hInst!=NULL)
  {

  FARPROC P;
  P=GetProcAddress(hInst,"fac");
  if(NULL != P)
  {
  int __fastcall (*fac)(int a,int b);
  fac = (int __fastcall (__cdecl*)(int a,int b))P;
  i = fac(StrToInt(Edit1->Text),StrToInt(Edit2->Text));
  ShowMessage("平方和是：" +AnsiString(i));
  }
  else
  {
  ShowMessage("Could not obtain function pointer!");
  }
  }
  FreeLibrary(hInst);
}

DLL文档里只有一个函数：
[code=C/C++][/code]
#pragma argsused
extern "C" __declspec(dllexport) int fac(int a,int b);
int WINAPI DllEntryPoint(HINSTANCE hinst, unsigned long reason, void* lpReserved)
{
  return 1;
}
//---------------------------------------
int fac(int a,int b)
{
  return pow(a,2)+pow(b,2);
}

为什么P的返回值是NULL呢？搞不懂呢！！

------解决方案--------------------
既然你调用的时候指定的约定是fastcall，那么DLL中函数的声明和定义也指定成fastcall，这样才能匹配。如：

C/C++ code

extern "C" __declspec(dllexport) int __fastcall fac(int a,int b);
int WINAPI DllEntryPoint(HINSTANCE hinst, unsigned long reason, void* lpReserved)
{
  return 1;
}
//---------------------------------------
int __fastcall fac(int a,int b)
{
  return pow(a,2)+pow(b,2);
}