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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) (none)

Notes

For two-way comparisons, binary operators may be more suitable.

Example

#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/#";
    demo(p1.compare(p2), p1, p2);
    demo(p1.compare("a/b/_"), p1, "a/b/_");
}

Output:

"/a/b/" > "/a/b/#"
"/a/b/" < "a/b/_"

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