如何在C中删除bstr类型 [英] how to delete bstr types in C

问题描述

这是矿山结构

  typedef   struct 消息
{

BSTR序列号；
_bstr_t时间戳记；
_bstr_t状态；
_bstr_t数据；


} MESSAGE，* PMESSAGE;

 typedef   struct  MESSAGENODE
{
PMESSAGE消息；
MESSAGENODE * pNext;
} MESSAGENODE，* PMESSAGENODE; 

delete函数删除bstr变量

 PMESSAGE pMess;
 while (((pMess = GetMachineMessage())！= NULL)
{
如果(pMess->数据& pMess->序列号)
{
删除 [] pMess->数据； // 错误错误C2440:删除":无法从"_bstr_t"转换为无效*" 
}
删除 pMess；
} 

这是获取机器消息

 PMESSAGE Message :: GetMachineMessage( void )
{
wLog-> WriteDebugLog(" )；
EnterCriticalSection(& MessageQueueCS);
PMESSAGENODE pRetNode;
如果(MessageQueueFront == NULL)
{
pRetNode = NULL;
}
其他
{
pRetNode = MessageQueueFront;
MessageQueueFront = pRetNode-> pNext;
如果(MessageQueueFront == NULL)
{
MessageQueueBack = NULL;
}
其他 如果(MessageQueueFront-> pNext == NULL)
{
MessageQueueBack = NULL;
}
}

LeaveCriticalSection(& MessageQueueCS);
如果(pRetNode == NULL)
{

wLog-> WriteErrorLog(" );
返回 NULL；
}
PMESSAGE pRet = pRetNode-> Message;
删除 pRetNode；
wLog-> WriteDebugLog(" )；
返回 pRet;
} 

解决方案

您不能(请参见Sergey答案)并且不能删除它.
_bstr_t是C++ 类，它包装了BSTR字符串(因此，Data是类的实例，即是对象，而不是指针，则无法删除它).
适当时，它会自动调用SysFreeString(在您的情况下，可能是pMess删除).
请参见"_bstr_t类" [typedef struct MESSAGE { BSTR SerialNo; _bstr_t TimeStampIs; _bstr_t Status; _bstr_t Data; } MESSAGE, *PMESSAGE; typedef struct MESSAGENODE { PMESSAGE Message; MESSAGENODE* pNext; } MESSAGENODE, *PMESSAGENODE;

delete function to delete the bstr variable

PMESSAGE pMess;
	while((pMess = GetMachineMessage()) != NULL)
	{
		if(pMess->Data && pMess->SerialNo)
		{
			delete[] pMess->Data;//error here error C2440: 'delete' : cannot convert from '_bstr_t' to 'void *' 
		}
		delete pMess;
	}

This is get machine message

PMESSAGE Message::GetMachineMessage(void)
{
	wLog->WriteDebugLog("Enter GetServerMessage");
	EnterCriticalSection(&MessageQueueCS);
	PMESSAGENODE pRetNode;
	if(MessageQueueFront == NULL)
	{
		pRetNode = NULL;
	} 
	else 
	{
		pRetNode = MessageQueueFront;
		MessageQueueFront = pRetNode->pNext;
		if(MessageQueueFront == NULL)
		{
			MessageQueueBack = NULL;
		} 
		else if(MessageQueueFront->pNext == NULL)
		{
			MessageQueueBack = NULL;
		}
	}

	LeaveCriticalSection(&MessageQueueCS);
	if(pRetNode == NULL) 
	{

		wLog->WriteErrorLog("OUT::GetServerMessage");
		return NULL;
	}
	PMESSAGE pRet = pRetNode->Message;
	delete pRetNode;
	wLog->WriteDebugLog("Exit GetServerMessage");
	return pRet;
}

解决方案

You cannot (see Sergey answer) and must NOT delete it.
_bstr_t is a C++ class that wraps a BSTR string (hence Data is an instance of a class, that is a object, not a pointer, you cannot delete it).
It automatically calls SysFreeString when appropriate (in your case, possibly, on pMess deletion).
See "_bstr_t Class"[^] at MSDN.

Here is the exact answer: you cannot delete any types at all, you can only delete instances of types (objects).

(Sorry if it looks too pedantic to you: you need to understand importance of accurate phrasing — this is the real purpose of this post.)

—SA

Your question has already been answered, but on the other hand SerialNo is a plain BSTR, so make sure you call SysFreeString for that, before you delete the MESSAGE object.

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