An application sends a CB_DIR message to add a list of filenames to the list box of a combo box.
CB_DIR wParam = (WPARAM) (UINT) uAttrs; // file attributes lParam = (LPARAM) (LPCTSTR) lpszFileSpec; // address of filename
| Value | Meaning | 
| DDL_ARCHIVE | Includes archived files. | 
| DDL_DIRECTORY | Includes subdirectories. Subdirectory names are enclosed in square brackets ([ ]). | 
| DDL_DRIVES | Includes drives. Drives are listed in the form [-x-], where x is the drive letter. | 
| DDL_EXCLUSIVE | Includes only files with the specified attributes. By default, read-write files are listed even if DDL_READWRITE is not specified. | 
| DDL_HIDDEN | Includes hidden files. | 
| DDL_READONLY | Includes read-only files. | 
| DDL_READWRITE | Includes read-write files with no additional attributes. | 
| DDL_SYSTEM | Includes system files. | 
The return value is the zero-based index of the last filename added to the list. If an error occurs, the return value is CB_ERR. If insufficient space is available to store the new strings, it is CB_ERRSPACE.
CB_ADDSTRING, CB_INSERTSTRING, DlgDirList, DlgDirListComboBox