Ubuntu 18.04 安装 clang++

Question

如何正确设置 clang 以在 Ubuntu 18.04 上使用 c++ std 库？ 我已经安装了一堆其他线程中建议的库 但没有成功。我还安装了两个 gcc 编译器（7,9） 使用 update-alternative 在它们之间切换。还有 Clang-6、Clang-9 和 llvm-9 已安装。

我安装的一些库

sudo apt install libstdc++-9-dev
sudo apt install libc++-9-dev
sudo apt install g++-7-multilib  
sudo apt install g++-9-multilib

我认为还有更多，但结果保持不变。

#include <iostream>

int main()
{
    std::cout << "Hello World\n";
}  

编译

clang++-9 hello_world.cpp
clang++ hello_world.cpp
clang++-9 -stdlib=libstdc++ hello_world.cpp
clang++ -stdlib=libstdc++ hello_world.cpp

所有产品

hello_world.cpp:2:10: fatal error: 'iostream' file not found

我发现了很多关于这个主题的帖子，但大多数都是在 Windows 或 macOS 上 或 8 岁。还有this 博文。我可能错过了一些东西 非常明显，希望有人能指出我正确的方向。

我是通过以下方式安装clang的，但我不记得确切的顺序：

sudo add-apt-repository ppa:ubuntu-toolchain-r/test
sudo apt install clang libclang-dev
sudo apt-get install libclang-9-dev 
sudo apt-get install clang-9
sudo apt-get install clang++-9

在 cmets 中建议尝试编译 clang++ -v hello_world.cpp 给出以下输出：

$ clang++ hello_world.cpp -v 
clang version 6.0.0-1ubuntu2 (tags/RELEASE_600/final)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Found candidate GCC installation: /usr/bin/../lib/gcc/i686-linux-gnu/8
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/10
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/6
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/6.5.0
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/7.5.0
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/8
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/9
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/10
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/9
Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/10
Candidate multilib: .;@m64
Selected multilib: .;@m64
 "/usr/lib/llvm-6.0/bin/clang" -cc1 -triple x86_64-pc-linux-gnu -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names -main-file-name hello_world.cpp -mrelocation-model static -mthread-model posix -mdisable-fp-elim -fmath-errno -masm-verbose -mconstructor-aliases -munwind-tables -fuse-init-array -target-cpu x86-64 -dwarf-column-info -debugger-tuning=gdb -v -resource-dir /usr/lib/llvm-6.0/lib/clang/6.0.0 -internal-isystem /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++ -internal-isystem /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/x86_64-linux-gnu -internal-isystem /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/backward -internal-isystem /usr/include/clang/6.0.0/include/ -internal-isystem /usr/local/include -internal-isystem /usr/lib/llvm-6.0/lib/clang/6.0.0/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -fdeprecated-macro -fdebug-compilation-dir /mnt/My_Linux_Files/C++/test2/src -ferror-limit 19 -fmessage-length 80 -fobjc-runtime=gcc -fcxx-exceptions -fexceptions -fdiagnostics-show-option -fcolor-diagnostics -o /tmp/hello_world-0f22e3.o -x c++ hello_world.cpp
clang -cc1 version 6.0.0 based upon LLVM 6.0.0 default target x86_64-pc-linux-gnu
ignoring nonexistent directory "/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/x86_64-linux-gnu"
ignoring nonexistent directory "/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/backward"
ignoring nonexistent directory "/include"
ignoring duplicate directory "/usr/include/clang/6.0.0/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++
 /usr/include/clang/6.0.0/include
 /usr/local/include
 /usr/include/x86_64-linux-gnu
 /usr/include
End of search list.
hello_world.cpp:2:10: fatal error: 'iostream' file not found
#include <iostream>
         ^~~~~~~~~~
1 error generated.

并使用 clang++-9：

$ clang++-9 hello_world.cpp -v 
clang version 9.0.0-2~ubuntu18.04.2 (tags/RELEASE_900/final)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Found candidate GCC installation: /usr/bin/../lib/gcc/i686-linux-gnu/8
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/10
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/6
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/6.5.0
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/7.5.0
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/8
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/9
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/10
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/9
Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/10
Candidate multilib: .;@m64
Selected multilib: .;@m64
 "/usr/lib/llvm-9/bin/clang" -cc1 -triple x86_64-pc-linux-gnu -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names -main-file-name hello_world.cpp -mrelocation-model static -mthread-model posix -mdisable-fp-elim -fmath-errno -masm-verbose -mconstructor-aliases -munwind-tables -fuse-init-array -target-cpu x86-64 -dwarf-column-info -debugger-tuning=gdb -v -resource-dir /usr/lib/llvm-9/lib/clang/9.0.0 -internal-isystem /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++ -internal-isystem /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/x86_64-linux-gnu -internal-isystem /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/backward -internal-isystem /usr/local/include -internal-isystem /usr/lib/llvm-9/lib/clang/9.0.0/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -fdeprecated-macro -fdebug-compilation-dir /mnt/My_Linux_Files/C++/test2/src -ferror-limit 19 -fmessage-length 0 -fobjc-runtime=gcc -fcxx-exceptions -fexceptions -fdiagnostics-show-option -fcolor-diagnostics -faddrsig -o /tmp/hello_world-9f4c00.o -x c++ hello_world.cpp
clang -cc1 version 9.0.0 based upon LLVM 9.0.0 default target x86_64-pc-linux-gnu
ignoring nonexistent directory "/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/x86_64-linux-gnu"
ignoring nonexistent directory "/usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/backward"
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++
 /usr/local/include
 /usr/lib/llvm-9/lib/clang/9.0.0/include
 /usr/include/x86_64-linux-gnu
 /usr/include
End of search list.
hello_world.cpp:2:10: fatal error: 'iostream' file not found
#include <iostream>
         ^~~~~~~~~~
1 error generated.

行：

Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/10

让我很困惑，clang 认为安装了 gcc-10 吗？因为我不 认为是：

$ find /usr/ -iname "*gcc-10*"
/usr/share/gcc-10
/usr/share/doc/gcc-10-base
/usr/share/doc/libgcc-10-dev
$

解决方案

按照 cmets 的建议，安装 libstdc++-10 解决了我的问题

Answer 1

在 Ubuntu 20.04 中，我设置了 by:

sudo apt update
sudo apt install clang

然后我编译并运行一个测试应用程序：

clang++ -o smeagol smeagol.cpp
./smeagol