ModbusTcp

#pragma pack(2)
struct MesCommuStruct
{
	WORD wStatus;
	DWORD dwTotal;
	DWORD dwError;
	DWORD dwGood;
	WORD wAlarm;
};
#pragma pack()

std::string sendMessage(const char* receive_message,int nLength)
{
	//目前收到的数据长度都是12，且必须等于12
	if (nLength!=12)
	{
		return std::string();
	}
	//数据转换时，需要将word用htons函数转化字节序，dword用htons转化字节序
	MesCommuStruct data;
	switch (CParameterCfg::m_SysStatus.m_nStatus)
	{
	case 0:
		data.wStatus = 0;
		data.wAlarm = htons(1);
		break;
	case 1:
		data.wStatus = htons(1);
		data.wAlarm = htons(1);
		break;
	case 2:
		data.wStatus = htons(1);
		data.wAlarm = htons(1);
		break;
	case 3:
		data.wStatus = htons(2);
		data.wAlarm = 0;
		break;
	default:
		break;
	}
	data.dwTotal = ntohl(_nTotalCount);
	data.dwError = ntohl(nErrorCount;
	data.dwGood = ntohl(nGoodCount);
//固定包头
std::string strResult;
for (int i = 0; i <= 4; i++)
{
	strResult.push_back((char)(receive_message[i]));
}

char strAddr[2], strCou[2];
strAddr[0] = receive_message[9];
strAddr[1] = receive_message[8];

strCou[0] = receive_message[11];
strCou[1] = receive_message[10];

unsigned short nStartAddress = *reinterpret_cast<unsigned short*>(strAddr)*2;
unsigned short nReadCount = *reinterpret_cast<unsigned short*>(strCou);

//一个word等于两个char
int nReadCharCount = nReadCount * 2;
//字符串数据区总长度
strResult.push_back(3+ nReadCharCount);
//设备地址
strResult.push_back(1);
//功能码
strResult.push_back(3);
//数据长度
strResult.push_back(nReadCharCount);

int nCount = 0;
for (int nIndex= nStartAddress;nIndex<sizeof(MesCommuStruct);nIndex++)
{
	if (nCount >= nReadCharCount)
	{
		break;
	}	
	strResult.push_back(reinterpret_cast<char*>(&data)[nIndex]);	
	nCount++;		
}

//超出有效数据，补0
for (int nIndex= nCount; nIndex<nReadCharCount;nIndex++)
{
	strResult.push_back(0);
}

return strResult; }