CC @alexbrainman

I think the failure of filepath.Rel(C:, C:\Windows) is intentional. godoc for Rel says:

An error is returned if targpath can't be made relative to basepath or if knowing the current working directory would be necessary to compute it.

C: is relative basepath - you would need to know the current directory to decide how to walk from it into C:\Windows.

The error message needs work (filled issue #13259 for that).

Please reopen, if you think I missed something.

Alex

I think C: means C:\ in Windows system. If the base directory is C:\Go then it must be written as filepath.Rel("C:\Go", "C:\Windows").

Like the example in filepath.Rel() that filepath.Rel("/a","/a/b/c") is b/c. I'll get the same result when I run it no matter where my current directory is. The "/a" means the current directory of "/a", that is "/a/."(dot) or simply "/a/". Likewise, C: should means the current directory of C: drive, that should be "C:."(dot) or simply "C:".

That said, the basepath in filepath.Rel() means the current folder(path) of the basepath. Rel() should add a Separator to the basepath if there is none.

Andrew

I think C: means C:\ in Windows system. ...

cmd.exe thinks differently:

C:\a>dir
 Volume in drive C has no label.
 Volume Serial Number is ABCD-EFGH

 Directory of C:\a

20/11/2015  04:30 PM    <DIR>          .
20/11/2015  04:30 PM    <DIR>          ..
               0 File(s)              0 bytes
               2 Dir(s)          305,408 bytes free

C:\a>dir c:
 Volume in drive C has no label.
 Volume Serial Number is ABCD-EFGH

 Directory of C:\a

20/11/2015  04:30 PM    <DIR>          .
20/11/2015  04:30 PM    <DIR>          ..
               0 File(s)              0 bytes
               2 Dir(s)          305,408 bytes free

C:\a>u:

U:\>dir c:
 Volume in drive C has no label.
 Volume Serial Number is ABCD-EFGH

 Directory of C:\a

20/11/2015  04:30 PM    <DIR>          .
20/11/2015  04:30 PM    <DIR>          ..
               0 File(s)              0 bytes
               2 Dir(s)          305,408 bytes free

U:\>c:

C:\a>dir c:
 Volume in drive C has no label.
 Volume Serial Number is ABCD-EFGH

 Directory of C:\a

20/11/2015  04:30 PM    <DIR>          .
20/11/2015  04:30 PM    <DIR>          ..
               0 File(s)              0 bytes
               2 Dir(s)          305,408 bytes free

C:\a>

Likewise, "C:" should means the current directory of "C:" drive, that should be "C:." or simply "C:".

This is wrong too. "C:" means "C:.".

Alex

I got it. You are right.

Maybe we need to note this special case in the Rel() document and let the user add the Separator themselves if they intend to the root of the VolumnName. Or make it default to root if it's just VolumnName.

Andrew

C: has no meaning unless you know what the "C: current directory" is. This is a general filepath concept. I don't see how it is useful to mention this is Rel documentation.

Alex