using System;

using System.IO;

​

Test(subPath: "c:/foo/bar", basePath: "c:/foo");        // with direct child (true)

Test(subPath: "c:/foo/bar/qux", basePath: "c:/foo");    // with level 2 child (true)

Test(subPath: "c:/foo", basePath: "c:/foo/bar");        // with args flipped (false)

Test(subPath: "c:/FOO/bar", basePath: "C:/foo");        // different case (result depends on platform)

Test(subPath: @"c:\foo\bar", basePath: @"c:\foo");      // with backslash (true)

Test(subPath: "c:/foo", basePath: "c:");                // drive letter only (true)

Test(subPath: "c:/foo/bar", basePath: "c:/foo/");       // trailing slash is ignored (true)

Test(subPath: "c:/foo/bar/", basePath: "c:/foo");       // trailing slash is ignored (true)

Test(subPath: "c:/foo/bar", basePath: "c:/foo/bar");    // same path (false)

Test(subPath: "d:/foo/bar", basePath: "c:/foo");        // different root (false)

Test(subPath: "c:/foo/.bar", basePath: "c:/foo");       // foldername starts with a dot (true)

Test(subPath: "c:/foo/../foo/bar", basePath: "c:/foo"); // you're breaking my balls here... (still works, though)

​

void Test(string subPath, string basePath) {

    var isSubPath = subPath.IsSubPathOf(basePath);

    var infix = isSubPath ? " " : " NOT ";

    Console.WriteLine($"'{subPath}'\tis{infix}a sub path of\t'{basePath}'");

}

​

public static class Ext {

    public static bool IsSubPathOf(this string subPath, string basePath) {

        var rel = Path.GetRelativePath(basePath.Replace('\\', '/'), subPath.Replace('\\', '/'));

        //Console.WriteLine($"\r\n{rel}\t"); // for debugging

        return rel != "."

            && rel != ".."

            && !rel.StartsWith("../")

            && !Path.IsPathRooted(rel);

    }

}

​