W3cubDocs

/C++

std::filesystem::path::compare

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

#include <iostream>
#include <filesystem>
#include <string_view>
namespace fs = std::filesystem;
 
void demo(fs::path p1, fs::path p2, std::string_view msg) {
    using std::cout;
    cout << p1;
    const int rc = p1.compare(p2); 
    if(rc < 0) cout << " < ";
    else if(rc > 0) cout << " > ";
    else cout << " == ";
    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