Difference between revisions of "cpp/filesystem/path/compare"
From cppreference.com
< cpp | filesystem | path
m (Text replace - "(===\s*Exceptions\s*===[^=]*)\(none\)" to "$1{{cpp/impldef exception item}}") |
(Improved example) |
||
| Line 47: | Line 47: | ||
#include <filesystem> | #include <filesystem> | ||
namespace fs = std::filesystem; | namespace fs = std::filesystem; | ||
| − | void demo( | + | |
| − | + | void demo(fs::path p1, fs::path p2, std::string msg) { | |
| − | else if(rc > 0) | + | using std::cout; |
| − | else if(rc == 0) | + | int rc = p1.compare(p2); |
| + | cout << p1; | ||
| + | if(rc < 0) cout << " < "; | ||
| + | else if(rc > 0) cout << " > "; | ||
| + | else if(rc == 0) cout << " == "; | ||
| + | cout << p2 << "\t: " << msg << '\n'; | ||
} | } | ||
| + | |||
int main() { | int main() { | ||
| − | + | demo("/a/b/", "/a/b/c", "simple"); | |
| − | + | demo("/a/b/../b", "/a/b", "no canonical conversion"); | |
| − | demo( | + | demo("/a/b", "/a/b/.", "no canonical conversion"); |
| − | demo | + | demo("/a/b/", "a/c", "absolute paths order after relative ones"); |
} | } | ||
|output= | |output= | ||
| − | "/a/b/" < "/a/b/c" | + | "/a/b/" < "/a/b/c" : simple |
| − | "/a/b/" > "a/c" | + | "/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 | ||
}} | }} | ||
Revision as of 02:15, 21 May 2021
| 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) May throw implementation-defined exceptions.
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(fs::path p1, fs::path p2, std::string msg) { using std::cout; int rc = p1.compare(p2); cout << p1; if(rc < 0) cout << " < "; else if(rc > 0) cout << " > "; else if(rc == 0) cout << " == "; cout << p2 << "\t: " << msg << '\n'; } int main() { 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/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
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) |
