C / C++ / MFC

CString strFilter;
strFilter += ...
strFilter += (TCHAR)'\0';   // last string
dlgFile.m_ofn.lpstrFilter = strFilter;

int AddToFilter(TCHAR* szFilter, int nSize, LPCTSTR szDescription, LPCTSTR szExtension)
{
   ASSERT(szFilter);
   ASSERT(szDescription);
   ASSERT(szExtension);
 
   _tcscpy(&szFilter[nSize], szDescription);
   int nLenDesc = _tcslen(szDescription);
 
   _tcscpy(&szFilter[nSize + nLenDesc + sizeof(TCHAR)], szExtension);
   int nLenExt = _tcslen(szExtension);
 
   return nSize + nLenDesc + nLenExt + (sizeof(TCHAR) * 2);
}

TCHAR szFilter[300] = _T("");
int nSize = 0;
 
if (IsWordInstalled())
   nSize = AddToFilter(szFilter, nSize, _T("Word"), _T("*.doc"));
 
if (IsExcelInstalled())
   nSize = AddToFilter(szFilter, nSize, _T("Excel"), _T("*.xls"));
 
AddToFilter(szFilter, nSize, _T("All Files"), _T("*.*"));