Difference between revisions of "cpp/filesystem/path/compare"
From cppreference.com
< cpp | filesystem | path
(normalization doesn't happen on paths when using the compare member function) |
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fs::path p2 = "/a/b/c"; | fs::path p2 = "/a/b/c"; | ||
demo(p1.compare(p2), p1, p2); | demo(p1.compare(p2), p1, p2); | ||
| − | demo(p1.compare("a/ | + | demo(p1.compare("a/b"), p1, "a/c"); |
} | } | ||
|output= | |output= | ||
Revision as of 14:32, 4 October 2020
| 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( 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)).
Contents |
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 |
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.
Exceptions
2-3) (none)
Notes
For two-way comparisons, binary operators may be more suitable.
Example
Run this code
#include <iostream> #include <filesystem> namespace fs = std::filesystem; void demo(int rc, fs::path p1, fs::path p2) { if(rc < 0) std::cout << p1 << " < " << p2 << '\n'; else if(rc > 0) std::cout << p1 << " > " << p2 << '\n'; else if(rc == 0) std::cout << p1 << " == " << p2 << '\n'; } int main() { fs::path p1 = "/a/b/"; // as if "a/b" for lexicographical iteration fs::path p2 = "/a/b/c"; demo(p1.compare(p2), p1, p2); demo(p1.compare("a/b"), p1, "a/c"); }
Output:
"/a/b/" < "/a/b/c" "/a/b/" < "a/c"
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 |
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) |
lexicographically compares two paths (function) |
