std::filesystem::path::lexically_normal, std::filesystem::path::lexically_relative, std::filesystem::path::lexically_proximate
From cppreference.com
< cpp | filesystem | path
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) |
2) Returns *this made relative to base.
- 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())
.
3) If the value of lexically_relative(base) is not an empty path, return it. Otherwise return *this.
Contents |
[edit] Parameters
(none)
[edit] Return value
1) The normal form of the path.
2) The relative form of the path.
3) The proximate form of the path.
[edit] Exceptions
May throw implementation-defined exceptions.
[edit] 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.
[edit] Example
Run this code
#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"); }
[edit] 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 |
[edit] See also
(C++17) |
composes a relative path (function) |