C# COM 调用C++编写的DLL函数各种参数传递问题

这两天一直在试着调用C++编写的Dll动态链接库来实现一些功能，初学总是遇见各种各样的问题，这次要实现一个改变系统时间的小功能，从而找到SetSystemTime这个系统API,
SetSystemTime的原型为：

BOOL WINAPI SetSystemTime(
  _In_  const SYSTEMTIME *lpSystemTime
);

typedef struct _SYSTEMTIME {
  WORD wYear;
  WORD wMonth;
  WORD wDayOfWeek;
  WORD wDay;
  WORD wHour;
  WORD wMinute;
  WORD wSecond;
  WORD wMilliseconds;
} SYSTEMTIME;

C# 实现

[StructLayout(LayoutKind.Sequential)]
public struct SYSTEMTIME
{
   public short wYear;
   public short wMonth;
   public short wDayOfWeek;
   public short wDay;
   public short wHour;
   public short wMinute;
   public short wSecond;
   public short wMilliseconds;
}
// top of class:
[DllImport("kernel32.dll", SetLastError = true)]
public static extern bool SetSystemTime(ref SYSTEMTIME theDateTime);
//..
//..
private bool DoSetSystemTime(DateTime newTime)
{   
   SYSTEMTIME st = new SYSTEMTIME();
   st.wDay = (short)newTime.Now.Day;
   st.wDayOfWeek = (short)newTime.Now.DayOfWeek;
   st.wHour = (short)newTime.Now.Hour;
   st.wMilliseconds = (short)newTime.Now.Millisecond;
   st.wMinute = (short)newTime.Now.Minute;
   st.wMonth = (short)newTime.Now.Month;
   st.wSecond = (short)newTime.Now.Second;
   st.wYear = (short)(newTime.Now.Year);  
   return SetSystemTime(ref st);
}

在调用C++编写的Dll动态链接库时常需要注意各种参数的传递问题，以下是摘自http://hi.baidu.com/yun0216/item/f7c856d227465738e3108fa3

1. 不返回值的参数

C++ 原型:

bool    SendNewSms(char *szTel, char *szMessage);

C#引用;

[DllImport( "CdmaCard.dll",EntryPoint="SendNewSms")]
public     static     extern    bool SendNewSms(string phone,string msg);

2. 带返回值(char *)

C++原型:

BOOL GetCardErrorMessage(char *szErrorMessage , int errorCode);

C#引用

[DllImport( "CdmaCard.dll",EntryPoint="GetCardErrorMessage")]
     public     static     extern    int GetCardErrorMessage(StringBuilder msg,int errorCode);



StringBuilder buf = new StringBuilder(1024);//指定的Buf大小必须大于可能的最大长度
       GetCardErrorMessage(buf,1);

3. 带返回值(其他类型)

C++原型:

   BOOL GetSmsSaveStation (int *nSmsStation);

C#引用

   [DllImport( "CdmaCard.dll",EntryPoint="GetSmsSaveStation")]
    public    static    extern   bool GetSmsSaveStation(ref int nStation);

4. 传递结构体指针(C++填充)
C++原型:
struct NET_INFO_STRUCT
{
   DWORD nDurationTime; //持续时间 
   double nReceiveByte; //接收字节
   double nSendByte;   //发送字节
};  
BOOL NetGetConnectDetail(NET_INFO_STRUCT *lpNetInfo);
C#引用
  
public struct NET_INFO_STRUCT
{
   public uint nDurationTime; //持续时间 
   public double nReceiveByte; //接收字节
   public double nSendByte;   //发送字节
}
[DllImport( "CdmaCard.dll",EntryPoint="NetGetConnectDetail")]
         public    static    extern   int NetGetConnectDetail(ref NET_INFO_STRUCT pNetInfo);
        
         NET_INFO_STRUCT netInfo = new NET_INFO_STRUCT();
         NetGetConnectDetail(ref netInfo); 
        
5. 传递结构体数组(C++来填充)
C++原型:
struct UIM_BOOK_STRUCT
{
   int UimIndex;
   char szName[15];
   char szPhone[21];
};
int ReadUimAllBook(UIM_BOOK_STRUCT lpUimBookItem[],int nMaxArraySize);

C#引用
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]//可以指定编码类型
public struct UIM_BOOK_STRUCT
{
   public int UimIndex;
   [MarshalAs(UnmanagedType.ByValTStr, SizeConst= 15)]
   public string szName;
   [MarshalAs(UnmanagedType.ByValTStr, SizeConst= 21)]
   public string szPhone;
};

[DllImport( "CdmaCard.dll",EntryPoint="ReadUimAllBook")]
public    static    extern   int ReadUimAllBook([Out] UIM_BOOK_STRUCT [] lpUimBookItem,int nMaxArraySize);

UIM_BOOK_STRUCT[] p = new UIM_BOOK_STRUCT[20];
int ret = ReadUimAllBook(p,p.Length);

6. 注意问题
类型不一致,会导致调用失败,
(1) long 类型,在C++中是4字节的整数,在C#中是8字节的整数;
(2) 字符串类型的设置不正确;