std::filesystem::path:: lexically_normal, std::filesystem::path:: lexically_relative, std::filesystem::path:: lexically_proximate
|
path lexically_normal
(
)
const
;
|
(1) | (since C++17) |
|
path lexically_relative
(
const
path
&
base
)
const
;
|
(2) | (since C++17) |
|
path lexically_proximate
(
const
path
&
base
)
const
;
|
(3) | (since C++17) |
-
- First, if root_name ( ) ! = base. root_name ( ) is true or is_absolute ( ) ! = base. is_absolute ( ) is true or ( ! has_root_directory ( ) && base. has_root_directory ( ) ) is true or any filename in relative_path ( ) or base. relative_path ( ) can be interpreted as a root-name , returns a default-constructed path.
- Otherwise, first determines the first mismatched element of * this and base as if by auto [ a, b ] = mismatch ( begin ( ) , end ( ) , base. begin ( ) , base. end ( ) ) , then
-
- if a == end ( ) and b == base. end ( ) , returns path ( "." ) ,
- otherwise, define N as the number of nonempty filename elements that are neither dot nor dot-dot in [ b, base. end ( ) ) , minus the number of dot-dot filename elements, If N < 0 , returns a default-constructed path,
- otherwise, if N = 0 and a == end ( ) || a - > empty ( ) , returns path ( "." ) ,
- otherwise returns an object composed from
-
- a default-constructed path ( ) followed by
- N applications of operator / = ( path ( ".." ) ) , followed by
-
one application of
operator
/
=
for each element in the half-open range
[a,end ( )).
Parameters
(none)
Return value
Exceptions
May throw implementation-defined exceptions.
Notes
These conversions are purely lexical. They do not check that the paths exist, do not follow symlinks, and do not access the filesystem at all. For symlink-following counterparts of
lexically_relative
and
lexically_proximate
, see
relative
and
proximate
.
On Windows, the returned
path
has backslashes (the preferred separators).
On POSIX, no filename in a relative path is acceptable as a root-name .
Example
#include <cassert> #include <filesystem> #include <iostream> namespace fs = std::filesystem; int main() { assert(fs::path("a/./b/..").lexically_normal() == "a/"); assert(fs::path("a/.///b/../").lexically_normal() == "a/"); assert(fs::path("/a/d").lexically_relative("/a/b/c") == "../../d"); assert(fs::path("/a/b/c").lexically_relative("/a/d") == "../b/c"); assert(fs::path("a/b/c").lexically_relative("a") == "b/c"); assert(fs::path("a/b/c").lexically_relative("a/b/c/x/y") == "../.."); assert(fs::path("a/b/c").lexically_relative("a/b/c") == "."); assert(fs::path("a/b").lexically_relative("c/d") == "../../a/b"); assert(fs::path("a/b").lexically_relative("/a/b") == ""); assert(fs::path("a/b").lexically_proximate("/a/b") == "a/b"); }
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 3070 | C++17 | a filename that can also be a root-name may cause surprising result | treated as error case |
| LWG 3096 | C++17 | trailing "/" and "/." are handled incorrectly | corrected |
See also
|
(C++17)
|
composes a relative path
(function) |