std::filesystem::path::compare
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C++
Feature test macros (C++20)
Concepts library (C++20)
Metaprogramming library (C++11)
Ranges library (C++20)
Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
Filesystem library
lexicographically compares two paths
(function) [edit]
std::filesystem::path
Path decomposition Non-member functions
Helper classes
path::compare
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)
(C++26)
int compare( const path& p ) const noexcept;
(1)
(since C++17)
int compare( const string_type& str ) const;
int compare( std::basic_string_view <value_type> str ) const;
(2)
(since C++17)
int compare( std::basic_string_view <value_type> str ) const;
int compare( const value_type* s ) const;
(3)
(since C++17)
Compares the lexical representations of the path and another path.
1) If root_name().native().compare(p.root_name().native()) is nonzero, returns that value.
Otherwise, if has_root_directory() != p.has_root_directory(), returns a value less than zero if
has_root_directory() is false and a value greater than zero otherwise. Otherwise returns a value less than, equal to or greater than 0 if the relative portion of the path (
relative_path()) is respectively lexicographically less than, equal to or greater than the relative portion of p (p.relative_path()). Comparison is performed element-wise, as if by iterating both paths from begin() to end() and comparing the result of native() for each element.2) Equivalent to compare(path(str)).
3) Equivalent to compare(path(s)).
[edit] Parameters
p
-
a path to compare to
str
-
a string or string view representing path to compare to
s
-
a null-terminated string representing path to compare to
[edit] Return value
A value less than 0 if the path is lexicographically less than the given path.
A value equal to 0 if the path is lexicographically equal to the given path.
A value greater than 0 if the path is lexicographically greater than the given path.
[edit] Exceptions
2,3) May throw implementation-defined exceptions.
[edit] Notes
For two-way comparisons, binary operators may be more suitable.
[edit] Example
Run this code
#include <filesystem> #include <iostream> #include <string_view> namespace fs = std::filesystem; void demo(fs::path p1, fs::path p2, std::string_view msg) { std::cout << p1; const int rc = p1.compare(p2); if (rc < 0) std::cout << " < "; else if (rc > 0) std::cout << " > "; else std::cout << " == "; std::cout << p2 << " \t: " << msg << '\n'; } int main() { demo("/a/b/", "/a/b/", "simple"); demo("/a/b/", "/a/b/c", "simple"); demo("/a/b/../b", "/a/b", "no canonical conversion"); demo("/a/b", "/a/b/.", "no canonical conversion"); demo("/a/b/", "a/c", "absolute paths order after relative ones"); }
Output:
"/a/b/" == "/a/b/" : simple "/a/b/" < "/a/b/c" : simple "/a/b/../b" > "/a/b" : no canonical conversion "/a/b" < "/a/b/." : no canonical conversion "/a/b/" > "a/c" : absolute paths order after relative ones
[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 2936 | C++17 | compared all path elements directly | root name and root directory handled separately |
[edit] See also
(C++17)(C++17)(until C++20)(C++17)(until C++20)(C++17)(until C++20)(C++17)(until C++20)(C++17)(until C++20)(C++20)
(function) [edit]