Dll c#的引入错误

[StructLayout(LayoutKind.Sequential)]
private struct RC_HARDWARE_INFO
{
int lSerialNumber;
int lCurrentNumber;
byte bDogType;
string bDogModel;
}

[DllImport("RCGrandDogW32.dll", EntryPoint = "RC_OpenDog", CharSet = CharSet.Ansi,
CallingConvention = CallingConvention.StdCall)]
private int RC_OpenDog(uint ulFlag, string pszProductName, int pDogHandle);

[DllImport("RCGrandDogW32.dll", EntryPoint = "RC_GetDogInfo", CharSet = CharSet.Ansi,
CallingConvention = CallingConvention.StdCall)]
private int RC_GetDogInfo(uint DogHandle, RC_HARDWARE_INFO pHardwareInfo, uint pulLen);
这个怎么老是出现
'MyDogClassTest.GrandDog.RC_openDog(uint, string, int)' must declare a body because it is not marked abstract, extern, or partial这个错误，高手帮一下，谢谢

private extern int RC_OpenDog(uint ulFlag, string pszProductName, int pDogHandle);

private extern int RC_GetDogInfo(uint DogHandle, RC_HARDWARE_INFO pHardwareInfo, uint pulLen);

加out参数试试