關於C#如何使用Prodave（實戰DllImport）

嚴格意義上講，此文不算OPC的範疇。起因是，另一個項目的PLC強人說，OPC慢，用prodave吧，好，用就用吧，裝好Prodave看是看其英文 資料，雖然英文不好，但好在這裡英文很簡單。好了，上網查了點資料，這裡還要感謝幾個朋友的幫忙，讓我對於C#與C++的資料結構有了更進 一步的認識，也學會了使用DllImport在本文的開頭，我要說明下，Prodave是西門子的通訊方式，即使我提供了Prodave6.dll，您不註冊也是 沒用用的，所以請使用西門子的安裝程式，哪裡下載？自己百度一下。不要來問我哪裡下載Prodave6.dll，也不要問我為什麼程式會報錯說沒 有註冊dll

下面開始進入本文。

（1）上來第一個函數，就是串連PLC的LoadConnection_ex6，在說明書裡描述如下：

LoadConnection_ex6
The basic LoadConnection_ex6 function initializes the adapter, checks if thE
driver is loaded, initializes the addresses that have been assigned parameters and
activates the selected interface.
LoadConnection_ex6 is used to set up a transport connection via MPI/PB- or IP
addresses (TCP/IP protocol)
int LoadConnection_ex6 (int ConNr, char* pAccessPoint, int ConTableLen,
CON_TABLE_TYPE * pConTable);
Parameters
ConNr
[in] Number of the connection (max. 64 connections).
pAccessPoint
[in] access point (zero-terminated) of the driver used, e.g. "S7ONLINE" for the MPI
driver or 0 (default).
ConTableLen
[in] length of the table of connections provided by the user in bytes
pConTablE
[in] pointer to address list of connected users; ‘Adr ==0’ is taken as the end mark of
the list.
#pragma pack(1)
typedef union {
unsigned char Mpi; // MPI/PB station address (2)
unsigned char Ip[4]; // IP address (192.168.0.1)
unsigned char Mac[6]; // MAC address (08-00-06-01-AA-BB)
} CON_ADR_TYPE;
typedef struct {
CON_ADR_TYPE Adr; // connection address
unsigned char AdrType; // Type of address: MPI/PB (1), IP (2), MAC (3)
unsigned char SlotNr; // Slot number
unsigned char RackNr; // Rack number
} CON_TABLE_TYPE;
#pragma pack(1)

好吧，起先其他的轉換網上都有 ，不難，但是出現了union共用體，恩C#沒有這個概念。怎麼辦？起先，參考網上的資料，採用

[StructLayout (LayoutKind.Explicit)]
struct S1
{
[FieldOffset(0)]
int a;
[FieldOffset(0)]
int b;
}