mex setup no longer finds compiler

I use Matlab 2019a and 2020b on Windows 10 with Visual Studio 2019. In the past I was able to build mex code, but now I can no longer find a compiler. The following changes might be relevant:

• Updated Microsoft Visual Studio Professional 2019 to version 16.8.4
• Installed Matlab Compiler on Matlab 2020b (no changes were made to 2019a, but it no longer works either)

After looking into this, it seems that calls to cmdReturns in msvcpp2019.xml always fail, and I haven't been able to find anyone with a similar issue. Here is the relevant output from mex -v -setup cpp:

... Looking for compiler 'Microsoft Visual C++ 2019' ...
... Looking for environment variable 'ProgramFiles(x86)' ...Yes ('C:\Program Files (x86)').
... Looking for file 'C:\Program Files (x86)\Microsoft Visual Studio\Installer\vswhere.exe' ...Yes.
... Executing command '"C:\Program Files (x86)\Microsoft Visual Studio\Installer\vswhere.exe" -version "[16.0,17.0)" -products Microsoft.VisualStudio.Product.Enterprise -property installationPath -format value' ...No.
... Looking for environment variable 'ProgramFiles(x86)' ...Yes ('C:\Program Files (x86)').
... Looking for file 'C:\Program Files (x86)\Microsoft Visual Studio\Installer\vswhere.exe' ...Yes.
... Executing command '"C:\Program Files (x86)\Microsoft Visual Studio\Installer\vswhere.exe" -version "[16.0,17.0)" -products Microsoft.VisualStudio.Product.Professional -property installationPath -format value' ...No.
... Looking for environment variable 'ProgramFiles(x86)' ...Yes ('C:\Program Files (x86)').
... Looking for file 'C:\Program Files (x86)\Microsoft Visual Studio\Installer\vswhere.exe' ...Yes.
... Executing command '"C:\Program Files (x86)\Microsoft Visual Studio\Installer\vswhere.exe" -version "[16.0,17.0)" -products Microsoft.VisualStudio.Product.Community -property installationPath -format value' ...No.
Did not find installed compiler 'Microsoft Visual C++ 2019'.

The call to vswhere.exe is failing; however, if I run the same command in a command prompt I do get output:

C:\>"C:\Program Files (x86)\Microsoft Visual Studio\Installer\vswhere.exe" -version "[16.0,17.0)" -products Microsoft.VisualStudio.Product.Professional -property installationPath -format value
C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional

To eliminate vswhere as the culprit, I added the following lines to msvcpp2019.xml:

<cmdReturns name="echo hello" />
<cmdReturns name="call echo hello" />

Which returns:

... Executing command 'echo hello' ...No.
... Executing command 'call echo hello' ...No.

So, it seems that cmdReturns always fails. What could be causing this?

Answer 1

[John Morgan]

I've finally fixed this! I noticed that whenever I started up a command pompt, the following appeared at the top of the window:

Microsoft Windows [Version 10.0.18363.1379]
(c) 2019 Microsoft Corporation. All rights reserved.
The system cannot find the path specified.

After searching for what could be causing the "The system cannot find the path specified." message I came across the advice to clear the following registry values:

• HKEY_CURRENT_USER\Software\Microsoft\Command Processor\AutoRun
• HKEY_LOCAL_MACHINE\Software\Microsoft\Command Processor\AutoRun

For me, the first value was populated with a conda_hook.bat file that didn't exist. After clearing the value, Matlab is able to find my compiler.

[Rihan Dsilva]

I have the same prolem. However, even after this fix, the problem persists. Was anyone able to solve this issue?

Answer 2

[Suryaansh Mata]

The issue looks similar to the one below. Give a try to the steps suggested for the same.

https://www.mathworks.com/matlabcentral/answers/328432-why-is-matlab-unable-to-find-the-microsoft-visual-c-2015-compiler-after-installing-microsoft-visua

Additionally, this might be due to issues with the key in the registry or environment variables. Reinstallation should add the right key in the registry and set the required env var

DISCLAIMER: These are my own views and in no way depict those of MathWorks.

[John Morgan]

Thanks for the response! I installed the latest SDK (10.0.19041.0), but am still having the same issue. I now have the following:

• C:\Program Files (x86)\Windows Kits\10\Include\10.0.10150.0
• C:\Program Files (x86)\Windows Kits\10\Include\10.0.10240.0
• C:\Program Files (x86)\Windows Kits\10\Include\10.0.10586.0
• C:\Program Files (x86)\Windows Kits\10\Include\10.0.14393.0
• C:\Program Files (x86)\Windows Kits\10\Include\10.0.18362.0
• C:\Program Files (x86)\Windows Kits\10\Include\10.0.19041.0

I'll try reinstalling next

[John Morgan]

I tried reinstalling and still get the same issue. I did the following:

1. Repair my Visual Studio installation
2. Reboot
3. Uninstall Matlab 2019a
4. Reboot
5. Uninstall Matlab 2020b
6. Reboot
7. Install Matlab 2020b to C:\MATLAB\R2020b

[zihui lang]

Suryaansh,

Hi there, I have a similar issue to John's but mine probabaly easier to solve. In my case, if I put the

C:\>"C:\Program Files (x86)\Microsoft Visual Studio\Installer\vswhere.exe" -version "[16.0,17.0)" -products Microsoft.VisualStudio.Product.Professional -property installationPath -format value

in my cmd. It won't gives me any return. I re-install my visual studio for several times and makes sure I'm including the vs2019 builder (MSDV v142) but this problem still shows up. When I put

mex -setup -v 

in my matlab, here is what it returns.

... Looking for compiler 'Microsoft Visual C++ 2019 (C)' ...
... Looking for environment variable 'ProgramFiles(x86)' ...Yes ('C:\Program Files (x86)').
... Looking for file 'C:\Program Files (x86)\Microsoft Visual Studio\Installer\vswhere.exe' ...Yes.
... Executing command '"C:\Program Files (x86)\Microsoft Visual Studio\Installer\vswhere.exe" -version "[16.0,17.0)" -products Microsoft.VisualStudio.Product.Enterprise -property installationPath -format value' ...No.
... Looking for environment variable 'ProgramFiles(x86)' ...Yes ('C:\Program Files (x86)').
... Looking for file 'C:\Program Files (x86)\Microsoft Visual Studio\Installer\vswhere.exe' ...Yes.
... Executing command '"C:\Program Files (x86)\Microsoft Visual Studio\Installer\vswhere.exe" -version "[16.0,17.0)" -products Microsoft.VisualStudio.Product.Professional -property installationPath -format value' ...No.
... Looking for environment variable 'ProgramFiles(x86)' ...Yes ('C:\Program Files (x86)').
... Looking for file 'C:\Program Files (x86)\Microsoft Visual Studio\Installer\vswhere.exe' ...Yes.
... Executing command '"C:\Program Files (x86)\Microsoft Visual Studio\Installer\vswhere.exe" -version "[16.0,17.0)" -products Microsoft.VisualStudio.Product.Community -property installationPath -format value' ...No.
Did not find installed compiler 'Microsoft Visual C++ 2019 (C)'.

I believe this is because my vswhere.exe is not working properly, but how should I fix it?

Thanks and looking forward to your reply,

Best,

Zihui

[Claudio Ferrara]

Hi @zihui lang I have the same problem now. Did you manage to solve the problem?

Answer 3

[Chris Marsh]

Hi,

I seem to have exactly the same problem.

I was using 2021b quite happily auto generating code from simulink (using VS 2019)

I then had to install 2021a (as another project was using this version)

After this Matlab (2021a or 2021b) cannot find my compiler.

I've tried re-installing everything VS and matlab version and rebooting countless times to no aval.

Help!!!

... Looking for compiler 'Microsoft Visual C++ 2019 (C)' ...
... Looking for environment variable 'ProgramFiles(x86)' ...Yes ('C:\Program Files (x86)').
... Looking for file 'C:\Program Files (x86)\Microsoft Visual Studio\Installer\vswhere.exe' ...Yes.
... Executing command '"C:\Program Files (x86)\Microsoft Visual Studio\Installer\vswhere.exe" -version "[16.0,17.0)" -products Microsoft.VisualStudio.Product.Enterprise -property installationPath -format value' ...No.
... Looking for environment variable 'ProgramFiles(x86)' ...Yes ('C:\Program Files (x86)').
... Looking for file 'C:\Program Files (x86)\Microsoft Visual Studio\Installer\vswhere.exe' ...Yes.
... Executing command '"C:\Program Files (x86)\Microsoft Visual Studio\Installer\vswhere.exe" -version "[16.0,17.0)" -products Microsoft.VisualStudio.Product.Professional -property installationPath -format value' ...No.
... Looking for environment variable 'ProgramFiles(x86)' ...Yes ('C:\Program Files (x86)').
... Looking for file 'C:\Program Files (x86)\Microsoft Visual Studio\Installer\vswhere.exe' ...Yes.
... Executing command '"C:\Program Files (x86)\Microsoft Visual Studio\Installer\vswhere.exe" -version "[16.0,17.0)" -products Microsoft.VisualStudio.Product.Community -property installationPath -format value' ...No.
Did not find installed compiler 'Microsoft Visual C++ 2019 (C)'.
Error using mex
Supported compiler not detected. You can install the freely available MinGW-w64 C/C++ compiler; see Install MinGW-w64 Compiler. For more options, visit https://www.mathworks.com/support/compilers.

[John Morgan]

Have you checked the registry values I mentioned in my answer? Here's the documentation:

If /D was NOT specified on the command line, then when CMD.EXE starts, it
looks for the following REG_SZ/REG_EXPAND_SZ registry variables, and if
either or both are present, they are executed first.

HKEY_LOCAL_MACHINE\Software\Microsoft\Command Processor\AutoRun

and/or

HKEY_CURRENT_USER\Software\Microsoft\Command Processor\AutoRun

If either results in an error then Matlab is unable to run vswhere. In my case it was trying to run a file that no longer existed

[Chris Marsh]

Hi,

Thanks for getting back to so fast.

So, forgive me, i didn't quite understand the "If /D was NOT specified on the command line, then when CMD.EXE starts,". part of your comment, could you explain a little more?

I looked at my registry

HKEY_LOCAL_MACHINE\Software\Microsoft\Command Processor\AutoRun

Which I believe is as expected / is correct.

The second part does not exist in my registry, which I'm not sure whether that is a problem or not ?

** Note lack of ...Microsoft\Command Processor\AutoRun

[John Morgan]

It's ok if there's no AutoRun variable; however, I believe the Command Processor folder should be there. This link might help: https://answers.microsoft.com/en-us/windows/forum/all/accidentally-deleted-command-processor-folder-in/2766c101-9e94-42e2-97e9-69def29da767 you may need to do a repair install