Re: CComBSTR, std::endl and stack overflow

"Heinz Ozwirk" <>
Wed, 9 Aug 2006 08:27:45 +0200
"Dilip" <> schrieb im Newsbeitrag

I have a STL map that looks like this:

typedef std::map<ATL::CComBSTR, SomeStructure* ss> structMap;
structMap actualMap;

Don't put CComBSTR into a map or any other STL container, directly. STL
containers assume that operator& returns the address of an object itself,
but CComBSTR (as well as some other COM wrappers like spart pointers) have
an overloaded operator&, which does not conform to the containers'
requirements. If you have to use CComBSTR or smart pointers in a container,
use CAdapt<>.

Probably this is not causing your problem, as others already mentioned, but
it is undefined behaviour which should be avoided.

ofstream ofs(...);
for (structMap::const_iterator itr = actualMap.begin(); itr !=
actualMap.end(); ++itr)
   CComBSTR const& thekey = itr->first;
   // use VC++ macro hocus-pocus to convert a BSTR to const char*
   ofs << W2A(thekey.m_str);
   ofs << std::endl;

If I comment out the first 2 lines inside the loop, everything works
fine (obviously I am priting the other members of SomeStructure).
Uncommenting them causes a stack overflow error deep in the bowels of
std::endl when it tries to flush the contents to the file. Is there
any known problems when W2A is called in a tight loop? My map can have
literally millions of entries.

One solution would be to use wofstream instead of ostream. As long as you
open the file in text mode, wofstream will convert unicode strings to the
current MBCS automatically, at least as long as you are using the new
implementation defined in <fstream> instead of the old one from <fstream.h>


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