Resolve Windows drive letter to a path (subst and network)

Question

I wonder if there is a universal way of resolving a path using a drive letter (such as X:\foo\bar.txt) into its equivalent UNC path, which might be one of the following:

• X:\foo\bar.txt if X: is a real drive (i.e. hard disk, USB stick, etc.)
• \\server\share\foo\bar.txt if X: is a network drive mounted on \\server\share
• C:\xyz\foo\bar.txt if X: is the result of a SUBST command mapping X: to C:\xyz

I know that there are partial solutions which will:

1. Resolve a network drive (see for instance question 556649 which relies on WNetGetUniversalName)

2. Resolve the SUBST drive letter (see QueryDosDevice which works as expected, but does not return UNC paths for things such as local drives or network drives).

Am I missing some straightforward way of implementing this drive letter resolution in Win32? Or do I really have to mess with both WNetGetUniversalName and QueryDosDevice to get what I need?

Answer 1

Yes, you would need to resolve the drive letter independently.

WNetGetUniversalName() comes close, but only works for drive letters that are mapped to actual UNC shares, which is not always the case. There is no single API function that does all of the work for you.

Answer 2

Here is a batch to translate drive letters to UNC paths or reverse substed paths. Not guaranteed it works though.

Example of use: script.cmd echo Z: Y: W:

@echo off
:: u is a variable containing all arguments of the current command line
set u=%*

:: enabledelayedexpansion: exclamation marks behave like percentage signs and enable
:: setting variables inside a loop
setlocal enabledelayedexpansion

:: parsing result of command subst
:: format:  I: => C:\foo\bar
:: variable %G will contain I: and variable H will contain C:\foo\bar
for /f "tokens=1* delims==> " %%G IN ('subst') do (
set drive=%%G
:: removing extra space
set drive=!drive:~0,2!
:: expanding H to a short path in order not to break the resulting command line
set subst=%%~sfH
:: replacing command line.
call set u=%%u:!drive!=!subst!%%
)

:: parsing result of command net use | findstr \\ ; this command is not easily tokenized because not always well-formatted
:: testing whether token 2 is a drive letter or a network path.
for /f "tokens=1,2,3 delims= " %%G IN ('net use ^| findstr \\') do (
set tok2=%%H
if "!tok2:~0,2!" == "\\" (
  set drive=%%G
  set subst=%%H
) else (
  set drive=%%H
  set subst=%%I
)
:: replacing command line.
call set u=%%u:!drive!=!subst!%%
)

call !u!