Append BStr

Mogaambo

Below is the code to append Bstr, but in debug mode it gives error ' ::SysFreeString(dest); ' and in release mode if i dont write ' ::SysFreeString(dest); ' it corrupts heap. What optimization i do. BSTR StringAppend(const BSTR dest,const BSTR src) { long destLen=::SysStringByteLen(dest); long srcLen=::SysStringByteLen(src); BSTR st3 = ::SysAllocStringByteLen(NULL,destLen+srcLen); try { if(st3==NULL) { throw "Insufficient Memory"; } else { wcscpy(st3, dest); wcscat(st3, src); ::SysFreeString(dest);// here it gives error in debug mode } } catch(char * error) { throw error; } return st3; }

“You will never be a leader unless you first learn to follow and be led.” –Tiorio "Coming together is a beginning, staying together is progress, and working together is success." Henry Ford

Madhu Nair 0

A const BSTR dest ? Why const ?

CPallini

Why are you freeing dest? :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]

_Superman_

I recommend CComBSTR::AppendBSTR or _bstr_t::operator+

«_Superman_» I love work. It gives me something to do between weekends.

KarstenK

why are you modifying a const input parameter ie deleting :mad:

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Mogaambo

CPallini wrote:

Why are you freeing dest?

Because if i do not free, it gives error that heap is violated in release mode and when i traced down it goes in the NULL condition.

“You will never be a leader unless you first learn to follow and be led.” –Tiorio "Coming together is a beginning, staying together is progress, and working together is success." Henry Ford

Mogaambo

KarstenK wrote:

why are you modifying a const input parameter ie deleting Mad

if i do not free all the memory gets exhausted.

“You will never be a leader unless you first learn to follow and be led.” –Tiorio "Coming together is a beginning, staying together is progress, and working together is success." Henry Ford

CPallini

Please show us the calling code. :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]

Mogaambo

Here is my calling code. value variable is of type BSTR BSTR GetNewRow() { value=GetLoggedInUser(); BSTR strComma=::SysAllocString(L","); BSTR strNewLine=::SysAllocString(L"\n"); value=StringAppend(value,strComma); value=StringAppend(value,strCategory); value=StringAppend(value,strComma); value=StringAppend(value,strItemName); value=StringAppend(value,strComma); value=StringAppend(value,strInstallDate); value=StringAppend(value,strComma); value=StringAppend(value,strVersion); value=StringAppend(value,strComma); value=StringAppend(value,strValue1); value=StringAppend(value,strComma); value=StringAppend(value,strValue2); value=StringAppend(value,strComma); value=StringAppend(value,strValue3); value=StringAppend(value,strNewLine); ::SysFreeString(strComma); ::SysFreeString(strNewLine); return value; }

“You will never be a leader unless you first learn to follow and be led.” –Tiorio "Coming together is a beginning, staying together is progress, and working together is success." Henry Ford

Rajesh R Subramanian

If it had to be released from within the function, why does it come into the function as a const parameter? Isn't this strikingly flashy, yelling "Hey look! I'm the silliest!"?

It is a crappy thing, but it's life -^ Carlo Pallini

KarstenK

To free up the strings is correct and necessary, BUT NOT in a subroutine. Make it after the sub routine call. :doh:

Press F1 for help or google it. Greetings from Germany

Mogaambo

This my calling code tell me where do i free BSTR GetNewRow() { value=GetLoggedInUser(); BSTR strComma=::SysAllocString(L","); BSTR strNewLine=::SysAllocString(L"\n"); value=StringAppend(value,strComma); value=StringAppend(value,strCategory); value=StringAppend(value,strComma); value=StringAppend(value,strItemName); value=StringAppend(value,strComma); value=StringAppend(value,strInstallDate); value=StringAppend(value,strComma); value=StringAppend(value,strVersion); value=StringAppend(value,strComma); value=StringAppend(value,strValue1); value=StringAppend(value,strComma); value=StringAppend(value,strValue2); value=StringAppend(value,strComma); value=StringAppend(value,strValue3); value=StringAppend(value,strNewLine); ::SysFreeString(strComma); ::SysFreeString(strNewLine); return value; }

“You will never be a leader unless you first learn to follow and be led.” –Tiorio "Coming together is a beginning, staying together is progress, and working together is success." Henry Ford

Madhu Nair 0

Mogaambo wrote:

BSTR strComma=::SysAllocString(L","); BSTR strNewLine=::SysAllocString(L"\n");

What about changing BSTR to _bstr_t ? Defined in comutil.h The MSDN link says that, A _bstr_t object encapsulates the BSTR data type. The class manages resource allocation and deallocation through function calls to SysAllocString and SysFreeString and other BSTR APIs when appropriate. The _bstr_t class uses reference counting to avoid excessive overhead. --++++++--- Use the += operator of _bstr_t to append characters to the end. if value is also declared as a type of _bstr_t then code can be re-written as,

value += strComma;
value += strNewLine;

:thumbsup:

modified on Wednesday, May 13, 2009 5:12 AM

CPallini

It looks like the problem is in your bad mixing of char and wchar calls: with the following line

BSTR st3 = ::SysAllocStringByteLen(NULL,destLen+srcLen);

you're allocating (destLen + srcLen + 1) bytes. while in the following calls

wcscpy(st3, dest);
wcscat(st3, src);

you need, (destLen + srcLen + 2) bytes. :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]

KarstenK

this is very lame code. You better make at first the output string with CString (or otherwise) and at last ::SysAllocString() :rolleyes:

Press F1 for help or google it. Greetings from Germany

Mogaambo · modified on Wednesday, May 13, 2009 5:12 AM

Thanks to all programming bees in helping me to solve my problems.

“You will never be a leader unless you first learn to follow and be led.” –Tiorio "Coming together is a beginning, staying together is progress, and working together is success." Henry Ford

Mogaambo

Thanks working great now . i don't know the +2 funda , actually i am c# developer but my firm wants me to develop project in c++. ::SysFreeString(dest); can i free this in StringAppend function itself or after my function returns.

“You will never be a leader unless you first learn to follow and be led.” –Tiorio "Coming together is a beginning, staying together is progress, and working together is success." Henry Ford

CPallini

Technically you can do it inside. However you probably should revise your design, for instance using a prototype like the following for your function:

HRESULT StringAppend( BSTR * pdst, const BSTR src);

or, better, using, as suggested, the handy _bstr_t wrapper. :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]

Mogaambo

1. BSTR * pdst why pointer here. BSTR is itself a pointer. 2. What code you have write for StringAppend function ? I want to take some idea from you.It would be very helpful for me.It's a humble request from a programmer to a professional.

“You will never be a leader unless you first learn to follow and be led.” –Tiorio "Coming together is a beginning, staying together is progress, and working together is success." Henry Ford

CPallini

Mogaambo wrote:

1. BSTR * pdst why pointer here. BSTR is itself a pointer.

Because the function will internally change the value of the original pointer, i.e. pdst is a INOUT parameter (this way you state clearly that the function may alter the original dst string).

Mogaambo wrote:

2. What code you have write for StringAppend function ?

Something like

HRESULT StringAppend(BSTR * pdest, const BSTR src)
{
if (pdest == NULL) return E_FAIL;
long destLen=::SysStringLen(*pdest);
long srcLen=::SysStringLen(src);

BSTR tmp = ::SysAllocStringLen(NULL,destLen+srcLen);
if( tmp == NULL) return E_FAIL;
wcscpy(tmp, *pdest);
wcscat(tmp, src);
::SysFreeString(*pdest);

pdest = &tmp;
*pdest = tmp;
return S_OK;
}

Beware: I didn't check this code (moreover I've used just the very basic E_FAIL failure return value, a good function should be more informative on failure.

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]

modified on Wednesday, May 13, 2009 8:02 AM