30 Input/output library [input.output]

30.10 File systems [filesystems]

30.10.8 Class path [fs.class.path]

30.10.8.1 Generic pathname format [fs.path.generic]

pathname:
	root-name root-directory relative-path

root-name:
	operating system dependent sequences of characters
	implementation-defined sequences of characters

root-directory:
	directory-separator

relative-path:
	filename
	filename directory-separator relative-path
	an empty path

filename:
	non-empty sequence of characters other than directory-separator characters

directory-separator:
	preferred-separator directory-separator
	fallback-separator directory-separator

preferred-separator:
	operating system dependent directory separator character

fallback-separator:
	/, if preferred-separator is not /
1
#
[ Note
:
Operating systems often place restrictions on the characters that may be used in a filename.
For wide portability, users may wish to limit filename characters to the POSIX Portable Filename Character Set:
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
a b c d e f g h i j k l m n o p q r s t u v w x y z
0 1 2 3 4 5 6 7 8 9 . _­ -
— end note
 ]
2
#
Except in a root-name, multiple successive directory-separator characters are considered to be the same as one directory-separator character.
3
#
The filename dot ([fs.def.filename]) is treated as a reference to the current directory.
The filename dot-dot ([fs.def.filename]) is treated as a reference to the parent directory.
What the filename dot-dot refers to relative to root-directory is implementation-defined.
Specific filenames may have special meanings for a particular operating system.
4
#
A root-name identifies the starting location for pathname resolution ([fs.def.pathres]).
If there are no operating system dependent root-names, at least one implementation-defined root-name is required.
[ Note
:
Many operating systems define a name beginning with two directory-separator characters as a root-name that identifies network or other resource locations.
Some operating systems define a single letter followed by a colon as a drive specifier – a root-name identifying a specific device such as a disk drive.
— end note
 ]
5
#
If a root-name is otherwise ambiguous, the possibility with the longest sequence of characters is chosen.
[ Note
:
On a POSIX-like operating system, it is impossible to have a root-name and a relative-path without an intervening root-directory element.
— end note
 ]