Installed Clang++3.6 on Ubuntu, Can't Select as Alternative

Installed clang++3.6 on Ubuntu, can't select as alternative

These work for me:

sudo update-alternatives --install /usr/bin/cc cc /usr/bin/clang-3.6 100
sudo update-alternatives --install /usr/bin/c++ c++ /usr/bin/clang++-3.6 100

Switching between GCC and Clang/LLVM using CMake

CMake honors the environment variables CC and CXX upon detecting the C and C++ compiler to use:

$ export CC=/usr/bin/clang
$ export CXX=/usr/bin/clang++
$ cmake ..
-- The C compiler identification is Clang
-- The CXX compiler identification is Clang

The compiler specific flags can be overridden by putting them into a make override file and pointing the CMAKE_USER_MAKE_RULES_OVERRIDE variable to it. Create a file ~/ClangOverrides.txt with the following contents:

SET (CMAKE_C_FLAGS_INIT                "-Wall -std=c99")
SET (CMAKE_C_FLAGS_DEBUG_INIT          "-g")
SET (CMAKE_C_FLAGS_MINSIZEREL_INIT     "-Os -DNDEBUG")
SET (CMAKE_C_FLAGS_RELEASE_INIT        "-O3 -DNDEBUG")
SET (CMAKE_C_FLAGS_RELWITHDEBINFO_INIT "-O2 -g")

SET (CMAKE_CXX_FLAGS_INIT                "-Wall")
SET (CMAKE_CXX_FLAGS_DEBUG_INIT          "-g")
SET (CMAKE_CXX_FLAGS_MINSIZEREL_INIT     "-Os -DNDEBUG")
SET (CMAKE_CXX_FLAGS_RELEASE_INIT        "-O3 -DNDEBUG")
SET (CMAKE_CXX_FLAGS_RELWITHDEBINFO_INIT "-O2 -g")

The suffix _INIT will make CMake initialize the corresponding *_FLAGS variable with the given value. Then invoke cmake in the following way:

$ cmake -DCMAKE_USER_MAKE_RULES_OVERRIDE=~/ClangOverrides.txt ..

Finally to force the use of the LLVM binutils, set the internal variable _CMAKE_TOOLCHAIN_PREFIX. This variable is honored by the CMakeFindBinUtils module:

$ cmake -D_CMAKE_TOOLCHAIN_PREFIX=llvm- ..

Setting _CMAKE_TOOLCHAIN_LOCATION is no longer necessary for CMake version 3.9 or newer.

Putting this all together you can write a shell wrapper which sets up the environment variables CC and CXX and then invokes cmake with the mentioned variable overrides.

Also see this CMake FAQ on make override files.

How do you make clang++ not warn about variable length arrays?

error: variable length arrays are a C99 feature [-Werror,-Wvla-extension]
  int a[argc];
       ^
1 error generated.

clang++ helpfully tells you what flags generated the diagnostic. Just "invert" the flag, in this case: -Wno-vla-extension.

clang++ under QtCreator can't work with c++11

TEMPLATE = app
CONFIG += console
CONFIG -= app_bundle
CONFIG -= qt

SOURCES += main.cpp

LIBS += -stdlib=libc++

QMAKE_CXXFLAGS += -stdlib=libc++
QMAKE_CXXFLAGS += -std=c++11
QMAKE_CXXFLAGS += -mmacosx-version-min=10.7
QMAKE_LFLAGS += -mmacosx-version-min=10.7

I can compile the codes by this .pro file
But there are warning when you play with Qt library

ld: warning: directory not found for option ‘-F/Users/yyyy/Qt5.0.1/5.0.1/clang_64/qtbase/lib’
After some research, I find out this is a bug of Qt5
It is ok if you ignore this warning message even it is annoying

Swift on Linux: Make very first step work

I had the exact same problem. It turns out that I had added the ppa:ubuntu-toolchain-r/test repo in order to install g++-4.9 on my Mint distro (17.2). Once I purged the repository and restored various libraries to their original versions, swift finally worked for me.

Specifically, I had to run

sudo apt-get install ppa-purge
sudo ppa-purge -d trusty ppa:ubuntu-toolchain-r/test

While cleaning up, ppa-purge was complaining that in order to resolve conflicts, it would have to remove quite a few packages it could not find in the Ubuntu Trusty repo (including really core ones like build-essential, xorg, gcc, x11-xserver-utils...), so I made a note and reinstalled these right away after the purge. Just be very careful.

I think some of the libraries overridden when installing g++ 4.9 were creating a conflict. I've verified all this on a fresh Mint install too.

How can I install clang-format in Ubuntu?

clang-format is not available in the ubuntu-precise 12.04 but it is available in ubuntu
saucy http://packages.ubuntu.com/saucy/clang-format-3.4.

in order to find this package with the apt-cache we have to add below list into our repository list. Actually below list is generated for the singapore servers but if you want to look for your own country you can use http://repogen.simplylinux.ch/generate.php

After generating your list, you have to add them into your repository, you can learn how to do that by looking to here. https://help.ubuntu.com/community/Repositories/CommandLine

The list of packages are;

deb http://sg.archive.ubuntu.com/ubuntu/ saucy main restricted universe multiverse 

deb-src http://sg.archive.ubuntu.com/ubuntu/ saucy main restricted universe multiverse 

deb http://sg.archive.ubuntu.com/ubuntu/ saucy-security main restricted universe multiverse 

deb http://sg.archive.ubuntu.com/ubuntu/ saucy-updates main restricted universe multiverse 

deb http://sg.archive.ubuntu.com/ubuntu/ saucy-proposed main restricted universe multiverse 

deb http://sg.archive.ubuntu.com/ubuntu/ saucy-backports main restricted universe    multiverse 

deb-src http://sg.archive.ubuntu.com/ubuntu/ saucy-security main restricted universe multiverse 

deb-src http://sg.archive.ubuntu.com/ubuntu/ saucy-updates main restricted universe multiverse 

deb-src http://sg.archive.ubuntu.com/ubuntu/ saucy-proposed main restricted universe multiverse 

deb-src http://sg.archive.ubuntu.com/ubuntu/ saucy-backports main restricted universe multiverse 

Then you should search clang-format with below command first

sudo apt-cache search clang-format

Then, you can install which version you want to install such as;

sudo apt-get install clang-format-3.3

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