Fail to run example with error: ‘MATHBACKEND’ was not declared in this scope

I try to run the provided example that “simple-real-numbers.cpp”, but facing following error.
My editor is VS Code, on WSL, the Open FHE is intalled on Nov. 2 2022, I guess it’s the latest version.

In file included from /usr/local/include/openfhe/core/math/hal/bigintbackend.h:70,
                 from /usr/local/include/openfhe/core/math/hal.h:55,
                 from /usr/local/include/openfhe/core/openfhecore.h:41,
                 from /usr/local/include/openfhe/pke/openfhe.h:40,
                 from /home/lance/code/linkGDrive/2022-7-4_FHE_inference/cpp_test/test.cpp:38:
/usr/local/include/openfhe/core/math/hal/bigintfxd/backendfxd.h: In function ‘const string& GetMathBackendParameters()’:
/usr/local/include/openfhe/core/math/hal/bigintfxd/backendfxd.h:48:57: error: ‘MATHBACKEND’ was not declared in this scope
   48 |     static std::string id = "Backend " + std::to_string(MATHBACKEND) +
      |                                                         ^~~~~~~~~~~
/usr/local/include/openfhe/core/math/hal/bigintfxd/backendfxd.h:48:57: note: the macro ‘MATHBACKEND’ had not yet been defined
In file included from /usr/local/include/openfhe/core/math/hal.h:55,
                 from /usr/local/include/openfhe/core/openfhecore.h:41,
                 from /usr/local/include/openfhe/pke/openfhe.h:40,
                 from /home/lance/code/linkGDrive/2022-7-4_FHE_inference/cpp_test/test.cpp:38:
/usr/local/include/openfhe/core/math/hal/bigintbackend.h:75: note: it was later defined here
   75 |     #define MATHBACKEND 2
      | 

How to fix it?

I have just installed OpenFHE and successfully run simple-real-numbers in a brand new environment without even changing it. there may be some problems with your environment.
I would recommend to: