Re: Finding an element in a map -

From:

David Wilkinson <no-reply@effisols.com>

Newsgroups:

microsoft.public.vc.language

Date:

Mon, 09 Mar 2009 09:53:59 -0400

Message-ID:

<O0Lr$5LoJHA.4028@TK2MSFTNGP03.phx.gbl>

Rashmi wrote:

Hi,
I have a COM DLL application wherein I get the string values that come from
C# application in BSTR format.
I'm able to convert the BSTR to TCHAR* without any problems.
I'm using a map in my application which is of the format <TCHAR*, TCHAR*>. I
get some input values in BSTR format which I'm trying to convert into
TCHAR*and use it in map::find(). Even though I can print the converted TCHAR*
value, the maps find() function is always failing.
But Whenever I hard code the value for the TCHAR* pointer and then use it
in the find() function I'm able to get the value of the key.
I'm pasting a part of my code below:

map<TCHAR*, TCHAR*>::map mymap;
.....
BSTR bstrVal = L"Key1";
TCHAR* ptr = new TCHAR[(wcslen(bstrVal)+1)*sizeof(TCHAR)];
_stprintf(ptr, _T("%ws"), (LPCSTR)bstrVal);

map<TCHAR*, TCHAR*>::iterator it;
it = mymap.find(ptr);
if(it != mymap.end())
........
else
.........

In this part of code, it always go to the else part of it. And i cant change
the datatype TCHAR * to TCHAR static array as the size of the [in] variable
is unpredictabale

Rashmi:

IMHO, using c-style strings in a container is a Really Bad Idea. I would use
std::string or std::wstring or agnostic tstring

typedef std::basic_string<TCHAR> tstring;

--
David Wilkinson
Visual C++ MVP