Clang does not find <future> header when using libc++ [duplicate] - c++

Question

I am wondering what is the right/easy way to install a binary libc++ on Ubuntu, in my case Trusty aka 14.04?
On the LLVM web site there are apt packages http://apt.llvm.org/ and I have used these to install 3.9. However these packages don't seem to include libc++. I install the libc++-dev package but that seems to be a really old version. There are also binaries that can be downloaded http://llvm.org/releases/download.html#3.9.0. These do seem to contain libc++ but I'm not sure if I can just copy bits of this into places like /usr/include/c++/v1, in fact I'm not really sure what bits I would need to copy. I am aware I can use libc++ from an alternate location as documented here http://libcxx.llvm.org/docs/UsingLibcxx.html which I have tried. However I can't modify the build system of the large code base I work on to do this.
So is three any reason the apt packages don't include libc++ and any pointers to installing a binary would be gratefully recieved.

Answer 1

How to build libc++ on Ubuntu 16.04
I had a similar issue as you do. While testing clang with libstdc++ worked fine with C++11 and C++14 there still might be licensing issues with libstdc++. So I ended up installing Clang toolchain from their repos and compiling libc++ on Ubuntu 16.04.
Disclaimer: This post is summary of long search on how to build the libc++ on Ubuntu Linux. Many of the posts I found in 2017 were either outdated or described a partial solution on other systems e.g. CentOS. Links to these posts are:
Hacking with Clang llvm abi and llvm libc
Building Clang and libc++ on Ubuntu Linux
How to Build libcxx and libcxxabi by clang on CentOS 7
Here are the steps to build LLVM + Clang + libc++ from the 4.0 release branch:
Install the key of LLVM Repositories
# apt-get update && apt-get dist-upgrade -y && apt-get install -y vim curl && \
curl -q https://apt.llvm.org/llvm-snapshot.gpg.key |apt-key add -
Create a new new APT Repository File (you can also exclude 2 lines referring to v3.9 repos)
# cat > /etc/apt/sources.list.d/llvm-repos.list <<EOF
deb http://apt.llvm.org/xenial/ llvm-toolchain-xenial main
deb-src http://apt.llvm.org/xenial/ llvm-toolchain-xenial main
deb http://apt.llvm.org/xenial/ llvm-toolchain-xenial-3.9 main
deb-src http://apt.llvm.org/xenial/ llvm-toolchain-xenial-3.9 main
deb http://apt.llvm.org/xenial/ llvm-toolchain-xenial-4.0 main
deb-src http://apt.llvm.org/xenial/ llvm-toolchain-xenial-4.0 main
EOF
Install Clang and all Packages needed to build libc++ from LLVM repos
# apt-get update && apt-get install -y clang-4.0 clang-4.0-doc \
libclang-common-4.0-dev libclang-4.0-dev libclang1-4.0 libclang1-4.0-dbg \
libllvm4.0 libllvm4.0-dbg lldb-4.0 llvm-4.0 llvm-4.0-dev llvm-4.0-runtime \
clang-format-4.0 python-clang-4.0 liblldb-4.0-dev lld-4.0 libfuzzer-4.0-dev \
subversion cmake
Create an alternative for C++ compiler and linker. This is not a must, but lets you switch compilers or linkers if needed. Also some build files needed cc or c++ or clang++ as far as I remember. Keep in mind, that we switch to LLD linker as default:
update-alternatives --install /usr/bin/cc cc /usr/bin/clang-4.0 100 \
&& update-alternatives --install /usr/bin/c++ c++ /usr/bin/clang++-4.0 100 \
&& update-alternatives --install /usr/bin/clang++ clang++ /usr/bin/clang++-4.0 100 \
&& update-alternatives --install /usr/bin/clang clang /usr/bin/clang-4.0 100 \
&& update-alternatives --install /usr/bin/ld ld /usr/bin/ld.lld-4.0 10 \
&& update-alternatives --install /usr/bin/ld ld /usr/bin/ld.gold 20 \
&& update-alternatives --install /usr/bin/ld ld /usr/bin/ld.bfd 30 \
&& ld --version && echo 3 | update-alternatives --config ld && ld --version
Checkout sources of libc++ and libc++abi:
$ cd /tmp
$ svn co http://llvm.org/svn/llvm-project/libcxx/branches/release_40/ libcxx
$ svn co http://llvm.org/svn/llvm-project/libcxxabi/branches/release_40/ libcxxabi
$ mkdir -p libcxx/build libcxxabi/build
To run libc++ on Linux one needs ABI compatibility to the standard library, e.g. libstdc++. This is where libc++abi comes into game. The only problem is that it needs libc++ to be on the system for which it is build. Thus libc++ is built in 2 steps. First: without any ABI compatibility. But it will be used for bootstrapping of ABI lib and than the second step is to recompile libc++ with the proper ABI present on system:
Bootstraping => build libc++ without proper ABI:
cd /tmp/libcxx/build
cmake -DCMAKE_BUILD_TYPE=Release -DLLVM_CONFIG_PATH=/usr/bin/llvm-config-4.0\
-DCMAKE_INSTALL_PREFIX=/usr .. \
&& make install
Building libc++abi with libstdc++ compatible ABI:
cd /tmp/libcxxabi/build
CPP_INCLUDE_PATHS=echo | c++ -Wp,-v -x c++ - -fsyntax-only 2>&1 \
|grep ' /usr'|tr '\n' ' '|tr -s ' ' |tr ' ' ';'
CPP_INCLUDE_PATHS="/usr/include/c++/v1/;$CPP_INCLUDE_PATHS"
cmake -G "Unix Makefiles" -DLIBCXX_CXX_ABI=libstdc++ \
-DLIBCXX_LIBSUPCXX_INCLUDE_PATHS="$CPP_INCLUDE_PATHS" \
-DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=/usr \
-DLLVM_CONFIG_PATH=/usr/bin/llvm-config-4.0 \
-DLIBCXXABI_LIBCXX_INCLUDES=../../libcxx/include ..
make install
Rebuild libc++ with proper ABI lib deployed on system:
cd /tmp/libcxx/build
cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=/usr \
-DLIBCXX_CXX_ABI=libcxxabi -DLLVM_CONFIG_PATH=/usr/bin/llvm-config-4.0\
-DLIBCXX_CXX_ABI_INCLUDE_PATHS=../../libcxxabi/include .. \
&& make install
Create a test file to check whether everything works fine. IMO you should also test cerr stream, as previously it was not supported with the libc++abi and there were some segfaults. Please refer to this question.
create a test.cpp file:
#include <iostream>
int main()
{
using namespace std;
cout << "[OK] Hello world to cout!" << endl;
cerr << "[OK] Hello world to cerr!" << endl;
clog << "[OK] Hello world to clog!" << endl;
return 0;
}
And compile it and run it using this command line:
clang++ -std=c++11 -stdlib=libc++ -lc++abi test.cpp && ./a.out
Reason there is no package
I found libc++ packages for Ubuntu but they are a bit behind recent version: https://packages.ubuntu.com/xenial/libc++-dev
Why they are not current, I can't answer, but my guess is that LLVM+Clang can work with mostly any Standard Library, whereas libc++ as you see must be linked to particular runtime ABI and might heavily depend on available C runtime library. I agree there should be a package which covers 90% of the cases. May be this is just the lack of resources. Searching the mailing archive did not bring up anything special.

Answer 2

sudo apt-get update
sudo apt-get install libc++-dev

Answer 3

The accepted answer gave me some errors (it is Nov 2021 currently). Also, sudo apt install libc++-dev libc++abi-dev did not provide the latest libc++. Here is an alternate solution.
Use the LLVM apt package maintainer's script:
sudo bash -c "$(wget -O - https://apt.llvm.org/llvm.sh)"
This automatically sets up the apt repositories and gives you the latest LLVM toolchain.
clang-13 --version
Since you now have the latest LLVM packages available from http://apt.llvm.org you can install the latest libc++. First determine the latest version:
apt search libc++ | grep libc++
Then:
sudo apt install libc++-13-dev libc++abi-13-dev
Optionally, you can use update-alternatives to make your system use clang-13 instead of the default. There is a gist for that:
wget https://gist.githubusercontent.com/junkdog/70231d6953592cd6f27def59fe19e50d/raw/update-alternatives-clang.sh
chmod +x update-alternatives-clang.sh
sudo ./update-alternatives-clang.sh 13 1000
Now:
clang --version
Debian clang version 13.0.1-++20211110062941+9dc7d6d5e326-1~exp1~20211110183517.26
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

Answer 4

The easiest way to get a working libc++ is to install the entire 3.9.0 toolchain under /usr/local. This will allow /usr/local/bin/clang++ to find the headers correctly and also allow the linker to find /usr/local/lib/libc++.so.

Answer 5

check my shell-script automation version:
https://github.com/sailfish009/llvm_all
$ sudo apt-get install libffi-dev libedit-dev swig git
$ git clone https://github.com/sailfish009/llvm_all
$ git clone https://github.com/llvm/llvm-project
$ cd llvm_all
$ cp *.sh ../llvm-project/
$ cd ../llvm-project/
$ ./set.sh
$ ./install.sh
$ clang++ --version
clang version 11.0.0 (https://github.com/llvm/llvm-project 032251e34d17c1cbf21e7571514bb775ed5cdf30)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

Answer 6

Just build it yourself, as explained here. I added -D CMAKE_CXX_COMPILER=clang++ -D CMAKE_C_COMPILER=clang to use clang as the compiler:
$ git clone https://github.com/llvm/llvm-project.git
$ cd llvm-project
$ mkdir build
$ cmake -G Ninja -S runtimes -B build -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi;libunwind" -D CMAKE_CXX_COMPILER=clang++ -D CMAKE_C_COMPILER=clang # Configure for clang++
$ ninja -C build cxx cxxabi unwind # Build
$ ninja -C build check-cxx check-cxxabi check-unwind # Test
$ ninja -C build install-cxx install-cxxabi install-unwind # Install