30 Input/output library [input.output]

30.10 File systems [filesystems]

30.10.8 Class path [fs.class.path]

30.10.8.4 path members [fs.path.member]

30.10.8.4.11 path generation [fs.path.gen]

path lexically_normal() const;
1
#
Returns: A path whose pathname in the generic format is the normal form ([fs.def.normal.form]) of the pathname in the generic format of *this.
2
#
[ Example
: 
assert(path("foo/./bar/..").lexically_normal() == "foo/");
assert(path("foo/.///bar/../").lexically_normal() == "foo/");
The above assertions will succeed.
On Windows, the returned path's directory-separator characters will be backslashes rather than slashes, but that does not affect path equality.
— end example
 ]
path lexically_relative(const path& base) const;
3
#
Returns: *this made relative to base.
Does not resolve ([fs.def.pathres]) symlinks.
Does not first normalize ([fs.def.normal.form]) *this or base.
4
#
Effects: 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, returns path().
Determines the first mismatched element of *this and base as if by: 
auto [a, b] = mismatch(begin(), end(), base.begin(), base.end());
Then,
  • (4.1)
    if a == end() and b == base.end(), returns path("."); otherwise
  • (4.2)
    let n be the number of filename elements in [b, base.end()) that are not dot or dot-dot minus the number that are dot-dot.
    If n<0, returns path(); otherwise
  • (4.3)
    returns an object of class path that is default-constructed, followed by
    • (4.3.1)
      application of operator/=(path("..")) n times, and then
    • (4.3.2)
      application of operator/= for each element in [a, end()).
5
#
[ Example
: 
assert(path("/a/d").lexically_relative("/a/b/c") == "../../d");
assert(path("/a/b/c").lexically_relative("/a/d") == "../b/c");
assert(path("a/b/c").lexically_relative("a") == "b/c");
assert(path("a/b/c").lexically_relative("a/b/c/x/y") == "../..");
assert(path("a/b/c").lexically_relative("a/b/c") == ".");
assert(path("a/b").lexically_relative("c/d") == "../../a/b");
The above assertions will succeed.
On Windows, the returned path's directory-separator characters will be backslashes rather than slashes, but that does not affect path equality.
— end example
 ]
6
#
[ Note
:
If symlink following semantics are desired, use the operational function relative().
— end note
 ]
7
#
[ Note
:
If normalization ([fs.def.normal.form]) is needed to ensure consistent matching of elements, apply lexically_­normal() to *this, base, or both.
— end note
 ]
path lexically_proximate(const path& base) const;
8
#
Returns: If the value of lexically_­relative(base) is not an empty path, return it.
Otherwise return *this.
9
#
[ Note
:
If symlink following semantics are desired, use the operational function proximate().
— end note
 ]
10
#
[ Note
:
If normalization ([fs.def.normal.form]) is needed to ensure consistent matching of elements, apply lexically_­normal() to *this, base, or both.
— end note
 ]