General Guidelines for Supporting Long Filenames

The following general guidelines for working with long filenames apply to all file systems supported by the various Windows systems. An application that follows these guidelines can create valid names for files and directories regardless of the file system in use.

• You can include any character from the current code page in a name, but do not use a path separator, a character in the ASCII range 0 through 31, or any character disallowed by the specific file system. A name can contain characters from the extended character set (ASCII 128 through 255).
• Use the backslash (\), the forward slash (/), or both to separate components in a path.
• Use a period (.) to represent the current directory in a path.
• Use two consecutive periods (..) to represent the parent of the current directory in a path.
• Separate components in a directory name or in a filename with a period (.).
• The following characters are reserved for Windows and should not be used in directory names or filenames:

< > : " / \ |

• Do not use reserved words, such as aux, con, and prn, as filenames or directory names.
• The application should process a path as a null-terminated string. The maximum length for a path is given by MAX_PATH. The Unicode versions of the CreateDirectory, FindFirstFile, GetFileAttributes, and SetFileAttributes functions allow paths to exceed the MAX_PATH length if the path has the \\?\ or \\?\UNC\ prefix. These prefixes turn off path parsing. Use the \\?\ prefix with paths for local storage devices and the \\?\UNC\ prefix with paths having the Universal Naming Convention (UNC) format. An example of a UNC path is \\machine\sharename.
• Do not assume case sensitivity, because not all file systems distinguish case. For example, under NTFS, the filenames FILENAME and Filename are considered to be the names of two different files; under HPFS, however, these two filenames are considered to be the same, although the file system preserves the case as entered and allows the user to see mixed-case filenames.