Append BStr

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

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

BSTR tmp = ::SysAllocStringLen(NULL,destLen+srcLen); dude you haven't added +2 bytes, it is crashing as that of mine, but when i added +2 it is running fine, so whenever i want allocate BSTR do i have 2 add + bytes. BSTR tmp = ::SysAllocStringLen(NULL,destLen+srcLen+2);

“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

What code you have written if you have to append the BSTR. It's a humble request from programmer to 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:

dude you haven't added +2 bytes

I know, I don't need to (I'm using SysAllocStringLen, not SysAllocStringByteLen).

Mogaambo wrote:

it is crashing as that of mine, but when i added +2 it is running fine

This is very strange.

Mogaambo wrote:

so whenever i want allocate BSTR do i have 2 add + bytes

Nope. Even if your point about the crash is true (and is true, I know) this is a wrong conclusion. :)

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

I would first make a complete string in a CString or TCHAR-array and at last create a BSTR.

Press F1 for help or google it. Greetings from Germany

CPallini

I made a silly error in my code, now fixed (please see again the posted snippet). It should be OK now, the following test runs fine:

BSTR dest = SysAllocString(L"Hi ");
BSTR s1,s2,s3,s4;
s1 = SysAllocString(L"People, ");
s2 = SysAllocString(L"How do ");
s3 = SysAllocString(L"you ");
s4 = SysAllocString(L"do?");
HRESULT hr;
hr = StringAppend(&dest, s1);
hr = StringAppend(&dest, s2);
hr = StringAppend(&dest, s3);
hr = StringAppend(&dest, s4);

MessageBoxW(dest, L"Info");

SysFreeString(s1);
SysFreeString(s2);
SysFreeString(s3);
SysFreeString(s4);
SysFreeString(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]

Mogaambo

If you run your code in debug mode , it crashes at line where you freeing the variable, but runs in release mode.

“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

My test works fine in DEBUG mode on my machine. What inputs are you providing? :)

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]