Mex "Unable to determine MEX compiler"

I am trying to use mex -setup to use Visual Studio 2017 as my C++ compiler for my matlab2019a.

I installed VS2017 and when I use mex -setup, everyting seemed to be well :

>> mex -setup:C:\Users\userwzz\AppData\Roaming\MathWorks\MATLAB\R2019a\mex_C++_win64.xml C++

MEX configured to use 'Microsoft Visual C++ 2017' for C++ language compilation.

Warning: The MATLAB C and Fortran API has changed to support MATLAB

variables with more than 2^32-1 elements. You will be required

to update your code to utilize the new API.

You can find more information about this at:

https://www.mathworks.com/help/matlab/matlab_external/upgrading-mex-files-to-use-64-bit-api.html.

However, when I run:

>> proj = openProject(pwd);

>> webcoder.build.project(proj);

to use the compiler for my program, the error occured:

??? The library method 'images.internal.coder.buildable.Grayto8Buildable.updateBuildInfo' failed.

Caused by:

Unable to determine MEX compiler: use mex -setup to configure your system.

Code generation failed: View Error Report

Error using codegen

Any suggestions for my problem? Why my matlab can't determine the compile after mex setup VS2017 as my compile for C++?

Thanks.

[Fangjun Jiang]

Might it be that you've set up for C++, but not for C?

Just run "mex -setup" again