Is this a bug on Path.Combine?

Question

I want to make sure that path always ends with \ and I try to use Path.Combine as the code below.

I expect System.IO.Path.Combine("xxx", System.IO.Path.DirectorySeparatorChar.ToString()) to return xxx\ but it returns only \

The same goes for System.IO.Path.Combine("xxx", "\\", "zz") which I expect xxx\zz but it turns out to be \zz

Here are tests I have done. enter image description here

I am not sure if this is a desired behavior or it's a bug.

`Path.Combine` produces paths. a string ending with a `\\` isn't a valid path. — Damien_The_Unbeliever, Jan 29 '14 at 08:15
Maybe this will help http://stackoverflow.com/questions/53102/why-does-path-combine-not-properly-concatenate-filenames-that-start-with-path-di — user2771704, Jan 29 '14 at 08:16
Btw, why do you need "path always ends with \"? To concatenate path with file name? Then, well, this is for what you should use `Path.Combine` (when you use it, you don't care about '\' at the end, you see?). — Sinatr, Jan 29 '14 at 08:24
The value will be used as a parameter to an external exe file. Unfortunately, that exe file treats `C:\xxxx` as a file while `C:\xxxx\` as a path. — Anonymous, Jan 29 '14 at 09:09
@Selman22 as I stated on the question, I tested it with a few cases I could come up with. :) — Anonymous, Jan 29 '14 at 09:10
@Anonymous I understand but you should take a look at the documentation first :) — Selman Genç, Jan 29 '14 at 09:11

score 5 · Answer 1 · answered Jan 29 '14 at 08:14

This is defined behaviour of Path.Combine. If the second (or any subsequent) path is "rooted", i.e. starts with a path delimiter like '\' or 'c:', any previous parameters are ignored. From the documentation:

If path2 does not include a root (for example, if path2 does not start with a separator character or a drive specification), the result is a concatenation of the two paths, with an intervening separator character. If path2 includes a root, path2 is returned.

You should not use things like System.IO.Path.DirectorySeparatorChar when using Path.Combine, IMHO, it's whole point of being is to make path manipulation easier, not harder.

score 1 · Answer 2 · answered Jan 29 '14 at 08:15

Path.Combine combines paths. If the second parameter is a relative path, the paths are combined; if it is an absolute path, only the second parameter is returned (since combining absolute paths does not make sense). \ is an absolute path referring to the root directory.

What you want can more easily be achieved by

myPath = myPath.TrimEnd('\') + "\";

On the other hand, why do you need your path to end with a \? The whole point of Path.Combine is that you don't need to have paths ending with \. Note the following examples:

myPath = Path.Combine(@"C:\xxx", "zz");    // yields C:\xxx\zz
myPath = Path.Combine(@"C:\xxx\", "zz");   // also yields C:\xxx\zz

score 0 · Answer 3 · answered Jan 29 '14 at 08:15

From the documentation for Combine:

If the one of the subsequent paths is an absolute path, then the combine operation resets starting with that absolute path, discarding all previous combined paths.

Since \ is an absolute path, everything preceding it is discarded.

score 0 · Answer 4 · answered Jan 29 '14 at 08:16

0

It's documented behaviour. From the documentation for Path.Combine(string path1, string path2):

If path2 contains an absolute path, this method returns path2.

answered Jan 29 '14 at 08:16

Joe

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Is this a bug on Path.Combine?

4 Answers4