静态对象及其创建方法

debugcn 发表于 Dev

巴特

我的程序出现问题，我正在使用Embarcadero XE8 C ++构建器进行32位工作。

当我想使用一种方法将内容读/写到PLC（可编程逻辑控制器，通常用于与机器通信）时，我得到的对象是NULL。

我只是有一个Main表单，我想在其中创建与PLC的连接。

在我的主要我有：

static CEasyPLCHandler *pPLCHandler;

在同一页面上的方法中，我有：

long ReadWriteTest(void)
{
unsigned long ulStart;
PlcSymbolDesc *pSymbols;
unsigned long ulNumOfSymbols = 0;
int iNumOfVars = 2;
int i;
char **ppszVars = new char*[iNumOfVars];

for (i=0; i< iNumOfVars; i++)
    ppszVars[i] = new char[255];

long lResult = RESULT_FAILED;
lResult = pPLCHandler->GetAllItems(&pSymbols, &ulNumOfSymbols);
if (lResult == RESULT_OK)

当我调试时，它显示pPLCHandler = NULL

当我检查出哪里CEasyPLCHandle来的时候，我来到一个页面（我从库中包含了该页面），并看到以下几行：

class PLCH_DLL_DECL CEasyPLCHandler : public CPLCHandler
{
public:
    CEasyPLCHandler(RTS_HANDLE hLogFile = RTS_INVALID_HANDLE);
    CEasyPLCHandler(PlcConfig *pPlcConfig, PlcDeviceDesc *pDeviceDesc, RTS_HANDLE hLogFile = RTS_INVALID_HANDLE);
    CEasyPLCHandler(unsigned long ulId, char *pszIniFile, RTS_HANDLE hLogFile = RTS_INVALID_HANDLE);
    CEasyPLCHandler(char *pszPlcName, char *pszIniFile, RTS_HANDLE hLogFile = RTS_INVALID_HANDLE);
    virtual ~CEasyPLCHandler(void);

    // See PLCConfig.h for defines of pszProtocol
    // e.g. #define PLCC_DN_TCPIP_L2ROUTE   "Tcp/Ip (Level 2 Route)"
    virtual long ConnectTcpipViaGateway(char *pszGatewayIP, char *pszPlcIP, char *pszProtocol = PLCC_DN_TCPIP_L2ROUTE, int bMotorola = 0, int bLoadSymbols = 1, unsigned long ulTimeout = PLCHANDLER_USE_DEFAULT, unsigned long ulPort = 1200); 
    virtual long ConnectRs232ViaGateway(char *pszGatewayIP, short sPort, unsigned long ulBaudrate, int bMotorola = 0, int bLoadSymbols = 1, unsigned long ulTimeout = PLCHANDLER_USE_DEFAULT);
    virtual long ConnectRs232ViaGatewayEx(char *pszGatewayIP, short sPort, unsigned long ulBaudrate, int bMotorola = 0, int bLoadSymbols = 1, unsigned long ulTimeout = PLCHANDLER_USE_DEFAULT, EXT_RS232_PARAMStyp *pExtParams = NULL);
    virtual long ConnectTcpipViaArti(char *pszPlcIP, char *pszProtocol = PLCC_DN_TCPIP_L2ROUTE, int bMotorola = 0, int bLoadSymbols = 1, unsigned long ulTimeout = PLCHANDLER_USE_DEFAULT, unsigned long ulPort = 1200);
    virtual long ConnectRs232ViaArti(short sPort, unsigned long ulBaudrate, int bMotorola = 0, int bLoadSymbols = 1, unsigned long ulTimeout = PLCHANDLER_USE_DEFAULT);
    virtual long ConnectToSimulation(char *pszSdbFile, int bLoadSymbols = 1, unsigned long ulTimeout = PLCHANDLER_USE_DEFAULT);
    virtual long ConnectViaGateway3(char *pszGatewayIP, char *pszAddress, int bLoadSymbols = 1, unsigned long ulTimeout = PLCHANDLER_USE_DEFAULT);
    virtual long ConnectViaGateway3Ex(char *pszGatewayIP, unsigned long ulPort, char *pszAddress, int bLoadSymbols = 1, unsigned long ulTimeout = PLCHANDLER_USE_DEFAULT);
    virtual long ConnectViaArti3(char *pszAddress, int bLoadSymbols = 1, unsigned long ulTimeout = PLCHANDLER_USE_DEFAULT);
    virtual long ConnectToSimulation3(char *pszSdb3XmlFile, int bLoadSymbols = 1, unsigned long ulTimeout = PLCHANDLER_USE_DEFAULT);


    // Attention: The structure of the service must be known in detail! 
    //            An erroneous service might cause a crash of the PLC! 
    // Send own service to plc and receive reply
    virtual long SyncSendService(/*[In]*/ unsigned char *pbySend, /*[In]*/ unsigned long ulSendSize, /*[Out]*/ unsigned char **ppbyRecv, /*[Out]*/ unsigned long *pulRecvSize);
    // Send own service to plc
    virtual long AsyncSendService(/*[Out]*/ int *piInvokeId, /*[In]*/ unsigned char *pbySend, /*[In]*/ unsigned long ulSendSize, /*[In]*/ CPLCHandlerCallback *pAsyncServiceCallback = NULL);
    // Get service reply
    virtual long AsyncGetServiceReply(/*[In]*/ int *piInvokeId, /*[Out]*/ unsigned char **ppbyRecv, /*[Out]*/ unsigned long *pulRecvSize, long *plServiceResult);
    // Get SessionId for Device services (only used for GW3 and ARTI3) 
    virtual unsigned long GetDeviceSessionId(void);
};

那么如何创建该对象？

我添加了一行：

pPLCHandler = new CEasyPLCHandler(RTS_INVALID_HANDLE);

并得到一些未解决的外部错误：

[ilink32错误]错误：从C：\ USERS \ BART \ DOCUMENTS \ EMBARCADERO \ STUDIO \ PROJECTS \ REALTEST \ WIN32 \ DEBUG \ UNIT1.OBJ引用的未解决的外部'CEasyPLCHandler ::〜CEasyPLCHandler（）'

但是这些已经在另一个文件中了吗？他为什么不能使用这些？

避难所

作为...我不能拼写名字的希腊人，已经正确地说了，您不是在初始化指针。静态或全局简单变量（int，double，char及其指针）将始终被初始化为0，这NULL就是从那里来的。

为了正确地初始化静态对象，您要么需要使用指针，new要么使用诸如之类的东西static CEasyPLCHandler PLCHandler(RTS_INVALID_HANDLE);，它将构造该对象并为您保存新对象和后续对象delete（避免内存泄漏）。

但是，从外观上看，您缺少包含您的代码的实际共享库CEasyPLCHandler object（至少链接器告诉我的是这样）。

请记住，如果您决定使用自动静态对象，则需要使用.而不是进行访问->。

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