Clang 不知道 PTRDIFF_MAX？

Question

我正在升级我们的构建机器（从 Windows Server 2008 到 Windows 10）并且构建在旧机器上运行良好（使用 Visual Studio）。我在新机器上使用 VS Build Tools 运行它时遇到了一些问题（我试图避免需要 VS 许可证），所以我将它移植到使用 Clang。

构建使用 Flatbuffers，我已从 1.4.0 升级到 1.12.0。在构建过程中出现以下错误：

[2/70] Building CXX object CMakeFiles\polyphemus.dir\hardwareconfig.cpp.obj

FAILED: CMakeFiles/polyphemus.dir/hardwareconfig.cpp.obj 

C:\PROGRA~2\MICROS~1\2019\BUILDT~1\VC\Tools\Llvm\x64\bin\clang-cl.exe  /nologo -TP  -I"C:\Program Files (x86)\nanomsg\include\nanomsg" -I. -I"C:\Program Files (x86)\FlatBuffers\include" -IE:\JenkinsMIDEBLD\workspace\btaylor-new_build_node_CYC-268_2\polyphemus\include /DWIN32 /D_WINDOWS /GR /EHsc /Zi /Ob0 /Od /RTC1 -MDd /showIncludes /FoCMakeFiles\polyphemus.dir\hardwareconfig.cpp.obj /FdCMakeFiles\polyphemus.dir\polyphemus.pdb -c E:\JenkinsMIDEBLD\workspace\btaylor-new_build_node_CYC-268_2\polyphemus\hardwareconfig.cpp

In file included from E:\JenkinsMIDEBLD\workspace\btaylor-new_build_node_CYC-268_2\polyphemus\hardwareconfig.cpp:3:
In file included from .\hardwareconfig_generated.h:7:
In file included from C:\Program Files (x86)\FlatBuffers\include\flatbuffers/flatbuffers.h:20:
In file included from C:\Program Files (x86)\FlatBuffers\include\flatbuffers/base.h:45:
C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC\14.26.28801\include\algorithm(37,63): error: use of undeclared identifier 'PTRDIFF_MAX'
    return static_cast<ptrdiff_t>(_Min_value(static_cast<_CT>(PTRDIFF_MAX), static_cast<_CT>(_Value)));

没有定义 PTRDIFF_MAX 真的很奇怪，这表明 Flatbuffers 应该在其文件中完成 #include <cstdint>，但没有。这似乎会导致测试失败，所以我不敢相信这是一个未诊断的错误。果然，如果我将#include <cstdint> 添加到我的文件中，它们就会开始构建。不过，这似乎确实不是正确的解决方案-我无法相信 Flatbuffers 具有未记录的依赖项，您必须自己进行导入，这表明我做错了。请问有谁知道吗？

编辑：在 cmake 中显式打开 C++17（以及从那里在 clang 中）会在不涉及平面缓冲区的不同位置导致相同的错误：

In file included from E:\JenkinsMIDEBLD\workspace\btaylor-new_build_node_CYC-268_2\polyphemus\complexseries.cpp:2:
In file included from E:\JenkinsMIDEBLD\workspace\btaylor-new_build_node_CYC-268_2\polyphemus\include\polyphemus/complexseries.h:4:
In file included from C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC\14.26.28801\include\complex:12:
In file included from C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC\14.26.28801\include\sstream:11:
In file included from C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC\14.26.28801\include\istream:11:
In file included from C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC\14.26.28801\include\ostream:11:
In file included from C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC\14.26.28801\include\ios:11:
In file included from C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC\14.26.28801\include\xlocnum:16:
In file included from C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC\14.26.28801\include\streambuf:11:
In file included from C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC\14.26.28801\include\xiosbase:12:
In file included from C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC\14.26.28801\include\system_error:14:
In file included from C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC\14.26.28801\include\stdexcept:12:
C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC\14.26.28801\include\xstring(1258,47): error: use of undeclared identifier 'PTRDIFF_MAX'
        return _Min_value(static_cast<size_t>(PTRDIFF_MAX), static_cast<size_t>(-1) / sizeof(_Elem));

那是在我自己完成#include of 的文件中，所以我想这是一个红鲱鱼（也不是修复：-/）。

Answer 1

原来我的包含路径中有一个 stdint.h 版本，它指定它“仅用于 Microsoft Visual C++ 编译器！”。毫不奇怪，事实证明它不适用于 Clang。你会期望它要么灾难性地失败，要么无论如何都可以工作（它确实定义了 PTRDIFF_MAX），但我想这只会导致 Clang 非常非常困惑。

无论如何，如果我从包含路径中删除它，一切都会开始工作。