I'm running into a weird compilation error that my google-fu can't solve.

Whenever I try to compile any project with the Uno R4 Wifi board, I get this error(full output txt attached):

String.cpp: 127:39: error: 'FLT_MAX_10_EXP' was not declared in this scope
   static size_t const FLOAT_BUF_SIZE = FLT_MAX_10_EXP + FLT_MAX_DECIMAL_PLACES + 1 \* - *\ + 1 \* . *\ + 1 \* \0 *
   ^~~~~~~~~~~~~~
String.cpp:127: note  suggested alternative  __FLT_MAX_10_EXP__
   static size_t const FLOAT_BUF_SIZE = FLT_MAX_10_EXP + FLT_MAX_DECIMAL_PLACES + 1 \* - *\ + 1 \* . *\ + 1 \* \0 *
   ^~~~~~~~~~~~~~
   __FLT_MAX_10_EXP__

String.cpp: 129:25: error: size of array 'buf' is not an integral constant-expression
   char buf[FLOAT_BUF_SIZE]
String.cpp: In constructor arduino::String::String(double, unsigned char)

String.cpp: 136:40: error: 'DBL_MAX_10_EXP' was not declared in this scope
   static size_t const DOUBLE_BUF_SIZE = DBL_MAX_10_EXP + DBL_MAX_DECIMAL_PLACES + 1 \* - *\ + 1 \* . *\ + 1 \* \0 *
   ^~~~~~~~~~~~~~
String.cpp:136: note  suggested alternative  __DBL_MAX_10_EXP__
Error compiling core
Build failed for project 'UnoR4_Sandbox'
   static size_t const DOUBLE_BUF_SIZE = DBL_MAX_10_EXP + DBL_MAX_DECIMAL_PLACES + 1 \* - *\ + 1 \* . *\ + 1 \* \0 *
   ^~~~~~~~~~~~~~
   __DBL_MAX_10_EXP__ 

and a couple more errors from the same String.cpp file.

However if I switch to the Ardiuno Uno(R3) board, everything compiles without issue. Also to note, the project I'm compiling in the attached output is just a blank arduino project from the project wizard.

In case anyone asks, everything compiles without issue using the Arduino IDE 2. I've also attached full compile output from Arduino IDE 2.

Thanks in advance for any help.

Thanks for the updates.

Can you restart the Arduino IDE, or delete the cached core folder, so that it is forced to build the core again so we can see the full output of this part of the process?

Thanks for the logs.

Can you try adding a local board.txt file to your project (vMicro > Add Code > Add Local Board.txt) and paste in the contents of the attached file.

Then if you run Build > Clean Solution in Visual Studio, and try recompiling, it should compile exactly as the Arduino IDE is currently.

For adding attachments, you may need to update your session, which will be shown in the toolbar at the top of the forum with an "Update Session" button if it is needed.

I agree it is very odd, and can't currently understand why the error is showing in vMicro and not in the Arduino IDE, especially with the same command (though the difference of removing the -w flag should have no effect as it just supresses warnings).

Can you try....
1) Closing all Arduino IDE and VS instances (and anything with any of the String.cpp/.h or float.h files open in it)
2) Open VS, and use File > Open Arduino Project, and open the same INO you are using in the Arduino IDE
NOTE - Don't add in the Local board.txt entries to this project as they made no difference and should not be required
3) Run build > clean Solution (just to be sure the shared core cache is clear)
4) Run the build process...

If this doesn't work then you could try running the command for the String.cpp via the command line after the above..... just to check that it works as expected, though it should give the same error.

Okay, I solved the problem!

Only I have no idea why exactly this solved problem, and I'm posing this info here incase you might.

After repairing my VS2022 install failed to fix the problem, I noticed I had installed some Intel C++ compiler (Intel® oneAPI DPC++/C++ Compiler to be exact) to play with and forgot about.

After uninstalling that compiler and repairing V2022, problem solved!

I'm not smart enough nor experienced enough to understand what was going wrong, but you probably are, so I'm attaching the successful build output to this post in the chance it might help you in any future development.

Thanks for your help! Let me know if you'd like any more info.