I wanted to try and use clang instead of gcc on my Ubuntu system. I set up the most basic C++ project possible, with a minimal CMakeLists.txt:
cmake_minimum_required(VERSION 3.20)
project(pcb_engine)
add_executable(main main.cpp)
My main.cpp is also very simple:
#include <iostream>
int main() {
std::cout << "Hello World" << std::endl;
return 0;
}
No when I run g++ -o main_g++ ../main.cpp everything compiles just fine. Also, if I set my system's default compiler to be gcc and g++ using
sudo update-alternatives --config c++
sudo update-alternatives --config cc
and I run cmake .. and make from my build folder, everything works!
The error:
Now I switch to using clang and clang++ as my default compiler via the update-alternatives command and while the build file generation succeeds, the make command fails with the following error message:
fatal error: 'iostream' file not found
#include <iostream>
When I run clang++ -v -stdlib=libc++ -Wall ../main.cpp -o main_clang manually, I get a linker error:
Ubuntu clang version 14.0.0-1ubuntu1
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/11
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/12
Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/12
Candidate multilib: .;@m64
Selected multilib: .;@m64
"/usr/lib/llvm-14/bin/clang" -cc1 -triple x86_64-pc-linux-gnu -emit-obj -mrelax-all --mrelax-relocations -disable-free -clear-ast-before-backend -disable-llvm-verifier -discard-value-names -main-file-name main.cpp -mrelocation-model pic -pic-level 2 -pic-is-pie -mframe-pointer=all -fmath-errno -ffp-contract=on -fno-rounding-math -mconstructor-aliases -funwind-tables=2 -target-cpu x86-64 -tune-cpu generic -mllvm -treat-scalable-fixed-error-as-warning -debugger-tuning=gdb -v -fcoverage-compilation-dir=/home/ivan/Documents/TEST/build -resource-dir /usr/lib/llvm-14/lib/clang/14.0.0 -internal-isystem /usr/lib/llvm-14/bin/../include/c++/v1 -internal-isystem /usr/lib/llvm-14/lib/clang/14.0.0/include -internal-isystem /usr/local/include -internal-isystem /usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../x86_64-linux-gnu/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -Wall -fdeprecated-macro -fdebug-compilation-dir=/home/ivan/Documents/TEST/build -ferror-limit 19 -fgnuc-version=4.2.1 -fcxx-exceptions -fexceptions -fcolor-diagnostics -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o /tmp/main-482542.o -x c++ ../main.cpp
clang -cc1 version 14.0.0 based upon LLVM 14.0.0 default target x86_64-pc-linux-gnu
ignoring nonexistent directory "/usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../x86_64-linux-gnu/include"
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/lib/llvm-14/bin/../include/c++/v1
/usr/lib/llvm-14/lib/clang/14.0.0/include
/usr/local/include
/usr/include/x86_64-linux-gnu
/usr/include
End of search list.
"/usr/bin/ld" -pie -z relro --hash-style=gnu --build-id --eh-frame-hdr -m elf_x86_64 -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o main_clang /lib/x86_64-linux-gnu/Scrt1.o /lib/x86_64-linux-gnu/crti.o /usr/bin/../lib/gcc/x86_64-linux-gnu/12/crtbeginS.o -L/usr/bin/../lib/gcc/x86_64-linux-gnu/12 -L/usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../lib64 -L/lib/x86_64-linux-gnu -L/lib/../lib64 -L/usr/lib/x86_64-linux-gnu -L/usr/lib/../lib64 -L/usr/lib/llvm-14/bin/../lib -L/lib -L/usr/lib /tmp/main-482542.o -lc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc /usr/bin/../lib/gcc/x86_64-linux-gnu/12/crtendS.o /lib/x86_64-linux-gnu/crtn.o
/usr/bin/ld: /tmp/main-482542.o: undefined reference to symbol '__gxx_personality_v0'
/usr/bin/ld: /lib/x86_64-linux-gnu/libc++abi.so.1: error adding symbols: DSO missing from command line
clang: error: linker command failed with exit code 1 (use -v to see invocation)
The non-verbose error message:
/usr/bin/ld: /tmp/main-f39fec.o: undefined reference to symbol '__gxx_personality_v0'
/usr/bin/ld: /lib/x86_64-linux-gnu/libc++abi.so.1: error adding symbols: DSO missing from command line
Can anyone help me identify where to start fixing this?
Interestingly, when I run clang++ -v -stdlib=libstdc++ -Wall ../main.cpp -o main_clang (note the -stdlib=libstdc++ flag change to the gnu standard library), then I get the same simple fatal error: 'iostream' file not found error as with cmake! So there is a difference in the behavior with the two different standard c++ libraries...
The background:
I come from using gcc, and installed clang via get-apt install clang. I've read that clang does not come with its own standard C++ library, but I have trouble understanding the implications for me: Previously, I had issues with clang finding a correct standard library .so file... I tried some more installs and I have got the libstdc++.so (default gnu) and the libc++.so as well as libc++.a and libc++.abi.so in my /usr/lib/x86_64-linux-gnu folder with a correct symlink hierarchy. For some reason, after a system restart, the /usr/bin/ld: cannot find -lstdc++ error went away, and now I have this linker error where it seems that clang can not find the include header files when running cmake. Now, I am at the end of my limited wisdom.
