NAME

std::filesystem::path::lexically_normal,std::filesystem::path::lexically_relative, - std::filesystem::path::lexically_normal,std::filesystem::path::lexically_relative,

Synopsis

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)

1) Returns *this converted to normal form in its generic format
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.

Parameters

(none)

Return value

1) The normal form of the path
2) The relative form of the path
3) The proximate form of the path

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

// Run this code

#include <iostream>
#include <filesystem>
#include <cassert>
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 treated as error case
may cause surprising result
LWG 3096 C++17 trailing "/" and "/." are handled corrected
incorrectly