std::filesystem::path:: compare

From cppreference.com
C++
Filesystem library
Classes
Functions
File types
std::filesystem::path
Constants
Member functions
Path decomposition
Non-member functions
(until C++20) (until C++20) (until C++20) (until C++20) (until C++20) (C++20)
Helper Classes
(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 ( 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 ) ) .

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 <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

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)
Retrieved from " https://en.cppreference.com/mwiki/index.php?title=cpp/filesystem/path/compare&oldid=158016 "