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I'd like to use clang without GCC on Linux and without MSVC on Windows. My understanding is that this wasn't possible in the past due to:
However, my impression what that this should be possible with v8.0.0 as there is now a viable linker and a compatible STL library.
Unfortunately, I get different errors on Linux and Windows when exercising this scenario (see more info below).
Can you help me out with this? Unfortunately, I've found it a bit challenging to find a definitive answer through various searches.
Thanks for the help!
Test Code: test.cpp
#include <vector>
#include <iostream>
int main(void) {
std::vector<int> const v{ 1, 2, 3 };
std::cout << "Hello world\n";
std::cout << v[0] << "\n";
return 0;
}
Linux output
The following output is from Windows Subsystem for Linux, but the behavior is the same on a proper Linux install.
clang -v /mnt/c/Temp/test.cpp -I/mnt/c/Code/v3/Common/cpp/Clang/8/Tools/Clang/v8.0.0/Ubuntu/wsl/include/c++/v1
clang version 8.0.0 (tags/RELEASE_800/final)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /mnt/c/Code/v3/Common/cpp/Clang/8/Tools/Clang/v8.0.0/Ubuntu/wsl/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8.0.1
"/mnt/c/Code/v3/Common/cpp/Clang/8/Tools/Clang/v8.0.0/Ubuntu/wsl/bin/clang-8" -cc1 -triple x86_64-unknown-linux-gnu -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names -main-file-name test.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 /mnt/c/Code/v3/Common/cpp/Clang/8/Tools/Clang/v8.0.0/Ubuntu/wsl/lib/clang/8.0.0 -I /mnt/c/Code/v3/Common/cpp/Clang/8/Tools/Clang/v8.0.0/Ubuntu/wsl/include/c++/v1 -internal-isystem /usr/local/include -internal-isystem /mnt/c/Code/v3/Common/cpp/Clang/8/Tools/Clang/v8.0.0/Ubuntu/wsl/lib/clang/8.0.0/include -internal-externc-isystem /include -internal-externc-isystem /usr/include -fdeprecated-macro -fdebug-compilation-dir /mnt/c/Code/v3/Common/cpp/Clang/8 -ferror-limit 19 -fmessage-length 200 -fobjc-runtime=gcc -fcxx-exceptions -fexceptions -fdiagnostics-show-option -fcolor-diagnostics -o /tmp/test-284194.o -x c++ /mnt/c/Temp/test.cpp -faddrsig
clang -cc1 version 8.0.0 based upon LLVM 8.0.0 default target x86_64-unknown-linux-gnu
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include <...> search starts here:
/mnt/c/Code/v3/Common/cpp/Clang/8/Tools/Clang/v8.0.0/Ubuntu/wsl/include/c++/v1
/usr/local/include
/mnt/c/Code/v3/Common/cpp/Clang/8/Tools/Clang/v8.0.0/Ubuntu/wsl/lib/clang/8.0.0/include
/usr/include
End of search list.
In file included from /mnt/c/Temp/test.cpp:1:
In file included from /mnt/c/Code/v3/Common/cpp/Clang/8/Tools/Clang/v8.0.0/Ubuntu/wsl/include/c++/v1/vector:273:
/mnt/c/Code/v3/Common/cpp/Clang/8/Tools/Clang/v8.0.0/Ubuntu/wsl/include/c++/v1/__config:206:12: fatal error: 'features.h' file not found
# include <features.h>
^~~~~~~~~~~~
1 error generated.
Windows Output
clang -v c:\temp\test.cpp
clang version 8.0.0 (tags/RELEASE_800/final)
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: C:\Code\v3\Common\cpp\Clang\8\Tools\Clang\v8.0.0\Windows\DefaultEnv\bin
clang: warning: unable to find a Visual Studio installation; try running Clang from a developer command prompt [-Wmsvc-not-found]
"C:\\Code\\v3\\Common\\cpp\\Clang\\8\\Tools\\Clang\\v8.0.0\\Windows\\DefaultEnv\\bin\\clang.exe" -cc1 -triple x86_64-pc-windows-msvc19.11.0 -emit-obj -mrelax-all -mincremental-linker-compatible -disable-free -disable-llvm-verifier -discard-value-names -main-file-name test.cpp -mrelocation-model pic -pic-level 2 -mthread-model posix -fmath-errno -masm-verbose -mconstructor-aliases -munwind-tables -target-cpu x86-64 -dwarf-column-info -momit-leaf-frame-pointer -v -resource-dir "C:\\Code\\v3\\Common\\cpp\\Clang\\8\\Tools\\Clang\\v8.0.0\\Windows\\DefaultEnv\\lib\\clang\\8.0.0" -internal-isystem "C:\\Code\\v3\\Common\\cpp\\Clang\\8\\Tools\\Clang\\v8.0.0\\Windows\\DefaultEnv\\lib\\clang\\8.0.0\\include" -internal-isystem "C:\\Code\\v3\\Common\\cpp\\Clang\\8\\Tools\\Clang\\v8.0.0\\Windows\\DefaultEnv\\include\\c++\\v1" -internal-isystem "C:\\Code\\v3\\Common\\cpp\\Common\\Libraries\\C++\\Catch2\\v2.7.0" -internal-isystem "C:\\Code\\v3\\Common\\cpp\\Common\\Libraries\\C++\\GSL\\v2.0.0\\include" -fdeprecated-macro -fdebug-compilation-dir "C:\\Code\\v3\\Common\\cpp\\Clang\\8" -ferror-limit 19 -fmessage-length 200 -fno-use-cxa-atexit -fms-extensions -fms-compatibility -fms-compatibility-version=19.11 -std=c++14 -fdelayed-template-parsing -fobjc-runtime=gcc -fcxx-exceptions -fexceptions -fdiagnostics-show-option -fcolor-diagnostics -o "C:\\Users\\brownell\\AppData\\Local\\Temp\\test-9329b0.o" -x c++ "c:\\temp\\test.cpp" -faddrsig
clang -cc1 version 8.0.0 based upon LLVM 8.0.0 default target x86_64-pc-windows-msvc
#include "..." search starts here:
#include <...> search starts here:
C:\Code\v3\Common\cpp\Clang\8\Tools\Clang\v8.0.0\Windows\DefaultEnv\lib\clang\8.0.0\include
C:\Code\v3\Common\cpp\Clang\8\Tools\Clang\v8.0.0\Windows\DefaultEnv\include\c++\v1
C:\Code\v3\Common\cpp\Common\Libraries\C++\Catch2\v2.7.0
C:\Code\v3\Common\cpp\Common\Libraries\C++\GSL\v2.0.0\include
End of search list.
In file included from c:\temp\test.cpp:1:
In file included from C:\Code\v3\Common\cpp\Clang\8\Tools\Clang\v8.0.0\Windows\DefaultEnv\include\c++\v1\vector:274:
In file included from C:\Code\v3\Common\cpp\Clang\8\Tools\Clang\v8.0.0\Windows\DefaultEnv\include\c++\v1\iosfwd:96:
C:\Code\v3\Common\cpp\Clang\8\Tools\Clang\v8.0.0\Windows\DefaultEnv\include\c++\v1\wchar.h:119:15: fatal error: 'wchar.h' file not found
#include_next <wchar.h>
^~~~~~~~~
1 error generated.
837
By default, Clang uses the target x86_64-pc-windows-msvc when compiling on Windows. With this target, Clang will look for Microsoft's msvc linker on PATH and use it for linking. If you want to go that route, install Microsoft Visual Studio.
Clang is a completely separate compiler (written entirely from scratch, using LLVM). You don't need GCC to use Clang, as can be shown in the case of FreeBSD (they completely replaced GCC with Clang/LLVM and don't install GCC in the base anymore for licensing reasons).
The c++ code compiled by clang runs a lot faster than the same code compiled by MSVC. And I checked the ASM code, found out that clang automatically uses SIMD instructions for speed purposes.
If you want to use clang instead of GCC, you can add -DCMAKE_C_COMPILER=/path/to/clang -DCMAKE_CXX_COMPILER=/path/to/clang++ . You can also use ccmake , which provides a curses interface to configure CMake variables in an interactive manner.
On linux clag will default to using gnu's implementation of the standard library which is libstdc++. To use llvm's implementation - libc++ - you first need to install it. On ubuntu, for instance: sudo apt install libc++-9-dev libc++abi-9-dev. You might need to add the apple repos. Follow these instructions for more systems and latest versions. Then you need to explicit specify it when compiling: -stdlib=libc++. Please see https://libcxx.llvm.org/docs/UsingLibcxx.html
For linking install lld (sudo apt install lld-9) then specify it when compiling with -fuse-ld=lld
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