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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
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A const BSTR dest ?
Why const ?
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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]
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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
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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]
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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
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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]
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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
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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]
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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
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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
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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
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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]
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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]
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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
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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]
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I recommend CComBSTR::AppendBSTR or _bstr_t::operator+
«_Superman_»
I love work. It gives me something to do between weekends.
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why are you modifying a const input parameter ie deleting 
Press F1 for help or google it.
Greetings from Germany
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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
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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
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To free up the strings is correct and necessary, BUT NOT in a subroutine. Make it after the sub routine call. 
Press F1 for help or google it.
Greetings from Germany
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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
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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
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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
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this is very lame code. You better make at first the output string with CString (or otherwise) and at last ::SysAllocString() 
Press F1 for help or google it.
Greetings from Germany
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