Path.Combine()处理盘符的行为及背后原因探究

Great question! This behavior isn’t a random quirk—it’s intentional, and it ties directly to how Windows (and its DOS-era predecessors) handle file system paths. Let me break it down clearly:

The critical difference between C: and C:\ #

On Windows, C:\ explicitly points to the root directory of the C drive. But C: (without the trailing backslash) refers to the current working directory of the C drive—not the root.

For example:

• If you’re in D:\Projects in Command Prompt and run cd C:, you’ll switch to the last active working directory on the C drive (say, C:\Users\YourName\Documents).
• Typing dir file.txt here will look for C:\Users\YourName\Documents\file.txt, not C:\file.txt.

Path.Combine follows Windows’ native path semantics #

The core design goal of Path.Combine is to preserve the actual meaning of the paths you pass in, rather than forcing arbitrary "corrections." When you pass @"c:" as the first argument:

• It recognizes this as a drive-relative path (not a root path)
• Since it doesn’t end with a valid directory separator, it appends the separator only to combine with the next segment—but it never converts C: to C:\, because that would completely change the path’s intended target.

So Path.Combine(@"c:", @"file.txt") outputs C:file.txt because that’s exactly the path Windows would interpret as "the file named file.txt in the current working directory of the C drive."

Why this design makes sense #

If Path.Combine automatically turned C: into C:\, it would override the user’s actual intent. Countless scripts and applications rely on drive-relative paths to interact with a drive’s current working directory—breaking this behavior would break compatibility with decades of Windows software conventions.

If you want to target the root directory explicitly, just use @"C:\" instead of @"C:"—Path.Combine(@"C:\", @"file.txt") will correctly return C:\file.txt.

内容的提问来源于stack exchange，提问作者BytesOfMetal