Re: Append BStr - C / C++ / MFC Discussion Boards

Re: Append BStr

Madhu Nair12-May-09 21:27

Madhu Nair

12-May-09 21:27

A const BSTR dest ?
Why const ?

Re: Append BStr

CPallini12-May-09 21:31

CPallini

12-May-09 21:31

Why are you freeing dest?

Smile | :)

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Re: Append BStr

Mogaambo12-May-09 22:26

Mogaambo

12-May-09 22:26

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

Re: Append BStr

CPallini12-May-09 22:33

CPallini

12-May-09 22:33

Please show us the calling code.
Smile | :)

Re: Append BStr

Mogaambo12-May-09 22:36

Mogaambo

12-May-09 22:36

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

Re: Append BStr

CPallini12-May-09 23:14

CPallini

12-May-09 23:14

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.

Smile | :)

Re: Append BStr

Mogaambo12-May-09 23:54

Mogaambo

12-May-09 23:54

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

Re: Append BStr

CPallini13-May-09 0:06

CPallini

13-May-09 0:06

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.
Smile | :)

Re: Append BStr

Mogaambo13-May-09 0:19

Mogaambo

13-May-09 0:19

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

Re: Append BStr [modified]

CPallini13-May-09 0:39

CPallini

13-May-09 0:39

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.

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

Re: Append BStr

Mogaambo13-May-09 0:53

Mogaambo

13-May-09 0:53

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

Re: Append BStr

CPallini13-May-09 1:33

CPallini

13-May-09 1:33

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.
Smile | :)

Re: Append BStr

CPallini13-May-09 2:08

CPallini

13-May-09 2:08

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);

Re: Append BStr

Mogaambo13-May-09 2:37

Mogaambo

13-May-09 2:37

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

Re: Append BStr

CPallini13-May-09 2:43

CPallini

13-May-09 2:43

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

Re: Append BStr

«_Superman_»12-May-09 21:52

«_Superman_»

12-May-09 21:52

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

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

Re: Append BStr

KarstenK12-May-09 22:25

KarstenK

12-May-09 22:25

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

Press F1 for help or google it.
Greetings from Germany

Re: Append BStr

Mogaambo12-May-09 22:28

Mogaambo

12-May-09 22:28

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

Re: Append BStr

Rajesh R Subramanian12-May-09 22:37

Rajesh R Subramanian

12-May-09 22:37

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

Re: Append BStr

KarstenK12-May-09 22:41

KarstenK

12-May-09 22:41

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

Press F1 for help or google it.
Greetings from Germany

Re: Append BStr

Mogaambo12-May-09 22:51

Mogaambo

12-May-09 22:51

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

Re: Append BStr [modified]

Madhu Nair12-May-09 22:55

Madhu Nair

12-May-09 22:55

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;

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

Re: Append BStr

Mogaambo12-May-09 23:51

Mogaambo

12-May-09 23:51

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

Re: Append BStr

KarstenK12-May-09 23:47

KarstenK

12-May-09 23:47

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

Press F1 for help or google it.
Greetings from Germany

Re: Append BStr

Mogaambo13-May-09 1:20

Mogaambo

13-May-09 1:20

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

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