SHGetFileInfo not return the icon location - c++

Question

I try to extract the icon of file and return it to GetIconLocation of shell extension.
in general I change the icons of files (te.docx.xx) with the extension of xx and returns the icon of file without the xx. (for this I cretae temp file in temp directory with the original extension e.g te.docx)
my operating system is windows 7 x64.
my code is:
STDMETHODIMP CTxtIconShlExt::GetIconLocation (
UINT uFlags, LPTSTR szIconFile, UINT cchMax,
int* piIndex, UINT* pwFlags )
{
DWORD dwFileSizeLo, dwFileSizeHi;
DWORDLONG qwSize;
HANDLE hFile;
OutputDebugStringW(L"Hello world, from GetIconLocation !");
std::string strFilePath;
std::string tempFolder="c:\\.tmp";
std::string tempFile="tmpfile";
std::string fileWithOutDN;
SHFILEINFO retShFileInfo;
for(int i = 0; m_szFilename[i] != 0; i++)
{
strFilePath += m_szFilename[i];
}
fileWithOutDN= strFilePath.substr(0,strFilePath.size()-3 );
std::string extension = fileWithOutDN.substr(fileWithOutDN.find_last_of("."));
CreateDirectory(tempFolder.c_str(),NULL);
tempFile=tempFolder+"\\"+tempFile+extension;
GetFileAttributes(tempFile.c_str()); // from winbase.h
if(INVALID_FILE_ATTRIBUTES == GetFileAttributes(tempFile.c_str()) && GetLastError()==ERROR_FILE_NOT_FOUND)
{
//File not found
HANDLE h = CreateFile(tempFile.c_str(), // name of the file
GENERIC_WRITE, // open for writing
0, // sharing mode, none in this case
0, // use default security descriptor
CREATE_ALWAYS, // overwrite if exists
FILE_ATTRIBUTE_NORMAL,
0);
if (h)
{
CloseHandle(h);
}else
{
return S_FALSE; //faild to create file
}
}
ZeroMemory(&retShFileInfo, sizeof(SHFILEINFO));
CoInitialize(NULL);
SHGetFileInfo(tempFile.c_str(),256,&retShFileInfo,sizeof(SHFILEINFO),SHGFI_ICON | SHGFI_LARGEICON);
lstrcpyn ( szIconFile, retShFileInfo.szDisplayName, cchMax );
*piIndex = retShFileInfo.iIcon;
*pwFlags = 0;
return S_OK;
my problem is that the retShFileInfo.szDisplayName return an empty array (all items are zero), it should return full path to icon location.
I try to play with the combination of the flags but nothing was helpful