[MSVC] Bitcoin build failed due to bitcoin\src\fs.h(75,39): error C2039: 'u8string': is not a member of 'std' with msvc option /c++latest #26444

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Recently, we updated the commit of bitcoin for MSVC RWC testing, it failed to build due to the error like below with option /c++latest, could you please help take a look? Thanks.

bitcoin\src\fs.h(75,39): error C2039: 'u8string': is not a member of 'std' [F:\gitP\bitcoin\bitcoin\build_msvc\libbitcoin_qt\libbitcoin_qt.vcxproj]
       C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Tools\MSVC\14.29.30133\include\filesystem(39,1): message : see declaration of 'std' [F:\gitP\bitcoin\bitcoin\build_msvc\libbitcoin_qt\libbitcoin_qt.vcxproj]

Expected behavior

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Build successfully.

Actual behavior

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bitcoin\src\fs.h(75,39): error C2039: 'u8string': is not a member of 'std' [F:\gitP\bitcoin\bitcoin\build_msvc\libbitcoin_qt\libbitcoin_qt.vcxproj]
       C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Tools\MSVC\14.29.30133\include\filesystem(39,1): message : see declaration of 'std' [F:\gitP\bitcoin\bitcoin\build_msvc\libbitcoin_qt\libbitcoin_qt.vcxproj]

To reproduce

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1. git clone https://github.com/bitcoin/bitcoin F:\gitP\bitcoin\bitcoin
2. git -C "F:\gitP\bitcoin\bitcoin" fetch --recurse-submodules=no --force
3. git -C "F:\gitP\bitcoin\bitcoin" reset --hard 43e813cab266eef42e622519836f171f6a18d426
4. set CL= /std:c++latest
5. cd F:\gitP\bitcoin\bitcoin\build_msvc
6. py -3 msvc-autogen.py
7. set CL=%CL% /D_HAS_DEPRECATED_ALLOCATOR_MEMBERS /D_SILENCE_CXX20_U8PATH_DEPRECATION_WARNING /Zc:char8_t- /D_SILENCE_CXX23_ALIGNED_STORAGE_DEPRECATION_WARNING
8. set the vcpkg info and run bootstrap-vcpkg.bat and vcpkg integrate install, in my environment, as follows: cd F:\gitP\bitcoin\tools\vcpkg git -C "F:\gitP\bitcoin\tools\vcpkg" clean -xdf bootstrap-vcpkg.bat set path=%cd%;%path% vcpkg integrate install
9. switch to the directory: cd F:\gitP\bitcoin\bitcoin\build_msvc
10. msbuild /m /p:Platform=x64 /p:Configuration=Release /p:PlatformToolset=v142 bitcoin.sln /t:Rebuild

System information

<!-- What version of Bitcoin Core are you using, where did you get it (website, self-compiled, etc)? -->

the commit of Bitcoin: 43e813cab266eef42e622519836f171f6a18d426

<!-- What type of machine are you observing the error on (OS/CPU and disk type)? -->

OS: Windows Server 2022 Datacenter 21H2

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<!--- This is normally the contents of a `debug.log` or `config.log` file. Raw text or a link to a pastebin type site are preferred. -->

Detailed log: build.log

The only supported option right now is C++20, which is already set in https://github.com/bitcoin/bitcoin/blob/39f026b1ec17ef8100457ef46a1e4980767c0fe2/build_msvc/common.init.vcxproj.in#L90

Closing for now. Let us know if you have any other questions.

@MarcoFalke You mean that bitcoin doesn't support /c++latest, right?

Detailed log: build.log

** Visual Studio 2019 Developer Command Prompt v16.11.20

From https://github.com/bitcoin/bitcoin/blob/master/build_msvc/README.md:

Visual Studio 2022 is minimum required to build Bitcoin Core.

@MarcoFalke You mean that bitcoin doesn't support /c++latest, right?

It may happen to work, but the only supported C++ version is the one listed in build_msvc/common.init.vcxproj.in

@MarcoFalke Ok, I got it. Thanks for the reply.

@hebasto I noticed that your reply in other issues mentioned that Visual Studio 2022 is minimum required to build Bitcoin Core. In fact, although we are using VS2019, we will use the latest build of msvc to replace the corresponding msvc related files in the vs path before build the code. We will upgrade VS recently, and I will try to build under vs2022 at then, if there are still problems, I will ask for help here again. Thank you for your reply.

We will upgrade VS recently, and I will try to build under vs2022 at then

To avoid linker errors, please ensure that dependencies are also built with VS 2022, including Qt stuff.

We will upgrade VS recently, and I will try to build under vs2022 at then

To avoid linker errors, please ensure that dependencies are also built with VS 2022, including Qt stuff.

Ok, I got it.