Difference between revisions of "cpp/filesystem/path/lexically normal"

Latest revision as of 22:24, 5 September 2023

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.

#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

relativeproximate

(C++17)

composes a relative path
(function) [edit]

@@ Line 2: / Line 2: @@
 {{cpp/filesystem/path/navbar}}
 {{dcl begin}}
-{{dcl | since=c++17 | num=1 | 1=
+{{dcl|since=c++17|num=1|1=
 path lexically_normal() const;
 }}
-{{dcl | since=c++17 | num=2 | 1=
+{{dcl|since=c++17|num=2|1=
-path lexically_relative(const path& base) const;
+path lexically_relative( const path& base ) const;
 }}
-{{dcl | since=c++17 | num=3 | 1=
+{{dcl|since=c++17|num=3|1=
-path lexically_proximate(const path& base) const;
+path lexically_proximate( const path& base ) const;
 }}
 {{dcl end}}
-@1@ Returns {{tt|*this}} converted to [[cpp/filesystem/path|normal form]] in its generic format
+@1@ Returns {{c|*this}} converted to [[cpp/filesystem/path|normal form]] in its generic format.
-@2@ Returns {{tt|*this}} made relative to {{tt|base}}.
+@2@ Returns {{c|*this}} made relative to {{c|base}}.
-:* First, if {{c|root_name() !{{=}} base.root_name() {{!!}} is_absolute() !{{=}} base.is_absolute() {{!!}} (!has_root_directory() && base.has_root_directory())}}, returns a default-constructed path.
+:* First, if {{c|1=root_name() != base.root_name()}} is {{c|true}} or {{c|1=is_absolute() != base.is_absolute()}} is {{c|true}} or {{c|(!has_root_directory() && base.has_root_directory())}} is {{c|true}} or any filename in {{c|relative_path()}} or {{c|base.relative_path()}} can be interpreted as a {{spar|root-name}}, returns a default-constructed path.
-:* Otherwise, first determines the first mismatched element of {{tt|*this}} and {{tt|base}} as if by  {{c|auto [a, b] {{=}} mismatch(begin(), end(), base.begin(), base.end())}}, then
+:* Otherwise, first determines the first mismatched element of {{c|*this}} and {{c|base}} as if by {{c|auto [a, b] {{=}} mismatch(begin(), end(), base.begin(), base.end())}}, then
-::* if {{c|a {{==}} end()}} and {{c|b {{==}} base.end()}}, returns {{c|path(".")}};
+::* if {{c|a {{==}} end()}} and {{c|b {{==}} base.end()}}, returns {{c|path(".")}},
-::* otherwise, if the number of {{spar|dot-dot}} filename elements in {{c|[b, base.end())}} is greater than the number of filename elements that are neither {{spar|dot}} nor {{spar|dot-dot}}, returns a default-constructed path.
+::* otherwise, define {{math|N}} as the number of nonempty filename elements that are neither {{spar|dot}} nor {{spar|dot-dot}} in {{c|[b, base.end())}}, minus the number of {{spar|dot-dot}} filename elements, If {{math|N < 0}}, returns a default-constructed path,
+::* otherwise, if {{math|N {{=}} 0}} and {{c|a {{==}} end() {{!!}} a->empty()}}, returns {{c|path(".")}},
 ::* otherwise returns an object composed from
 :::* a default-constructed {{c|path()}} followed by
-:::* as many applications of {{c|operator/{{=}}(path(".."))}} as there were filename elements in {{c|[b, base.end())}} that are neither {{spar|dot}} nor {{spar|dot-dot}} minus number of {{spar|dot-dot}} elements in that range, followed by
+:::* {{math|N}} applications of {{c|operator/{{=}}(path(".."))}}, followed by
-:::* one application of {{c|1=operator/=}} for each element in the half-open range {{tt|[a, end())}}
+:::* one application of {{c|1=operator/=}} for each element in the half-open range {{range|a|end()}}.
-@3@ If the value of {{c|lexically_relative(base)}} is not an empty path, return it. Otherwise return {{tt|*this}}.
+@3@ If the value of {{c|lexically_relative(base)}} is not an empty path, return it. Otherwise return {{c|*this}}.
 ===Parameters===
@@ Line 29: / Line 30: @@
 ===Return value===
-@1@ The normal form of the path
+@1@ The normal form of the path.
-@2@ The relative form of the path
+@2@ The relative form of the path.
-@3@ The proximate form of the path
+@3@ The proximate form of the path.
-===Exceptions===
+{{cpp/impldef exception}}
-(none)
 ===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 {{tt|lexically_relative}} and {{tt|lexically_proximate}}, see {{ltt|cpp/filesystem/relative|relative}} and {{ltt|cpp/filesystem/relative|proximate}}.
-On Windows, the returned path has backslashes (the preferred separators),
+On Windows, the returned {{tt|path}} has backslashes (the preferred separators).
+On POSIX, no filename in a relative path is acceptable as a {{spar|root-name}}.
 ===Example===
-{{example|code=
+{{example
-#include <iostream>
+|code=
-#include <filesystem>
 #include <cassert>
+#include <filesystem>
+#include <iostream>
 namespace fs = std::filesystem;
 int main()
 {
-     assert(fs::path("foo/./bar/..").lexically_normal() == "foo/");
+     assert(fs::path("a/./b/..").lexically_normal() == "a/");
-     assert(fs::path("foo/.///bar/../").lexically_normal() == "foo/");
+     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");
@@ Line 59: / Line 61: @@
      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===
+{{dr list begin}}
+{{dr list item|wg=lwg|dr=3070|std=c++17|before=a filename that can also be a root-name may cause surprising result|after=treated as error case}}
+{{dr list item|wg=lwg|dr=3096|std=c++17|before=trailing "/" and "/." are handled incorrectly|after=corrected}}
+{{dr list end}}
 ===See also===
 {{dsc begin}}
-{{dsc inc | cpp/filesystem/dsc relative}}
+{{dsc inc|cpp/filesystem/dsc relative}}
 {{dsc end}}
-{{langlinks|ja|zh}}
+{{langlinks|de|es|ja|ru|zh}}

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Difference between revisions of "cpp/filesystem/path/lexically normal"

Latest revision as of 22:24, 5 September 2023

Contents

[edit] Parameters

[edit] Return value

[edit] Exceptions

[edit] Notes

[edit] Example

[edit] Defect reports

[edit] See also

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