What is the difference between DirectorySeparatorChar and AltDirectorySeparatorChar

Question

System.io.DirectorySeparatorChar returns the character "\" while System.io.AltDirectorySeparatorChar returns "/"

to be more specific what is the job of System.Io.AltDirectorySeparatorChar and when we use it?

Answer 1

From the documentation (https://learn.microsoft.com/en-us/dotnet/api/system.io.path.altdirectoryseparatorchar)

Provides a platform-specific alternate character used to separate directory levels in a path string that reflects a hierarchical file system organization.

You can use alt separator in your path strings the same way as you use normal separator. Like this:

static void Main(string[] args)
{
        string[] pathStrings =
        {
            @"C:\dir\subdir\file.txt",
            "C:/dir/subdir/file.txt",
            "/dir/subdir/file.txt"
        };

        foreach (var p in pathStrings)
        {
            var dir = Path.GetDirectoryName(p);
            var file = Path.GetFileName(p);
            Console.WriteLine($"{dir} {file}");
        }

}

And the output:

C:\dir\subdir file.txt
C:\dir\subdir file.txt
\dir\subdir file.txt

Answer 2

My understanding is that DirectorySeparatorChar is platform-specific default separator, while AltDirectorySeparatorChar is platform-independent universal separator.

On Windows : DirectorySeparatorChar is backslash, AltDirectorySeparatorChar is forward slash
On Unix-based : Both are forward slash

It is because Windows natively prefers backslash but also supports forward slash, while Unix-based systems only support forward slash. Practically, it means you can use either one.
I would personally prefer DirectorySeparatorChar, because I simply prefer backslash on Windows. But perhaps the best is to use Path.Combine and let the choice up to this method.