how to delete bstr types in C

Question

2.50/5 (2 votes)

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This is mine structure

C++

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

C++

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

C++

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;
}

Posted 25-Oct-12 5:07am

Tarun Batra

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Comments

unitrunker 25-Oct-12 11:55am

Why are you deleting a _bstr_t? The destructor for _bstr_t should call SysFreeString on the underlying BSTR. If you only want to release the Data portion you can do this:

SysFreeString(pMess->Data.Detach());

Sergey Alexandrovich Kryukov 25-Oct-12 16:48pm

Delete types? Are you sure? :-)
--SA

4 solutions

Solution 4

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.

Posted 25-Oct-12 19:51pm

Marius Bancila

Solution 1

Have you tried free() instead of delete?

Posted 25-Oct-12 5:26am

Charlie Cox

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CPallini · Accepted Answer · 2012-10-25T11:17:00

Solution 3

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.

Posted 25-Oct-12 11:17am

CPallini

Comments

Sergey Alexandrovich Kryukov 26-Oct-12 11:19am

Good point, a 5.
--SA

Sergey Alexandrovich Kryukov · Accepted Answer · 2012-10-25T10:47:00

Solution 2

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

Posted 25-Oct-12 10:47am

Sergey Alexandrovich Kryukov