= Compiling with clang :toc: :toc-placement!: toc::[] # Introduction When building with CMake it is possible to set the C and C++ compiler. This example is the same as the link:../A-hello-cmake[hello-cmake] example except that it shows the most basic method of changing the compiler from the default gcc to http://clang.llvm.org/[clang]. The files in this tutorial are below: ``` A-hello-cmake$ tree . ├── CMakeLists.txt ├── main.cpp ``` * CMakeLists.txt - Contains the CMake commands you wish to run * main.cpp - A simple "Hello World" cpp file. # Concepts ### Compiler Option CMake exposes options to control the programs used to compile and link your code. These programs include: * CMAKE_C_COMPILER - The program used to compile c code. * CMAKE_CXX_COMPILER - The program used to compile c++ code. * CMAKE_LINKER - The program used to link your binary. [NOTE] ==== In this example clang-3.6 is installed via the command `sudo apt-get install clang-3.6` ==== [NOTE] ==== This is the most basic and easiest way to invoke clang. Future examples will show better ways to invoke the compiler. ==== ### Setting Flags As described in the link:../F-build-type[Build Type] example, you can set CMake options using either a cmake gui or by passing from the command line. Below is an example of passing the compiler via the command line. [source,cmake] ---- cmake .. -DCMAKE_C_COMPILER=clang-3.6 -DCMAKE_CXX_COMPILER=clang++-3.6 ---- After setting these options when your run `make` clang will be used to compile your binary. This can be seen from the following lines in the make output. [source,bash] ---- /usr/bin/clang++-3.6 -o CMakeFiles/hello_cmake.dir/main.cpp.o -c /home/matrim/workspace/cmake-examples/01-basic/I-compiling-with-clang/main.cpp Linking CXX executable hello_cmake /usr/bin/cmake -E cmake_link_script CMakeFiles/hello_cmake.dir/link.txt --verbose=1 /usr/bin/clang++-3.6 CMakeFiles/hello_cmake.dir/main.cpp.o -o hello_cmake -rdynamic ---- # Building the Examples Below is sample output from building this example. [source,bash] ---- $ mkdir build.clang $ cd build.clang/ $ cmake .. -DCMAKE_C_COMPILER=clang-3.6 -DCMAKE_CXX_COMPILER=clang++-3.6 -- The C compiler identification is Clang 3.6.0 -- The CXX compiler identification is Clang 3.6.0 -- Check for working C compiler: /usr/bin/clang-3.6 -- Check for working C compiler: /usr/bin/clang-3.6 -- works -- Detecting C compiler ABI info -- Detecting C compiler ABI info - done -- Check for working CXX compiler: /usr/bin/clang++-3.6 -- Check for working CXX compiler: /usr/bin/clang++-3.6 -- works -- Detecting CXX compiler ABI info -- Detecting CXX compiler ABI info - done -- Configuring done -- Generating done -- Build files have been written to: /home/matrim/workspace/cmake-examples/01-basic/I-compiling-with-clang/build.clang $ make VERBOSE=1 /usr/bin/cmake -H/home/matrim/workspace/cmake-examples/01-basic/I-compiling-with-clang -B/home/matrim/workspace/cmake-examples/01-basic/I-compiling-with-clang/build.clang --check-build-system CMakeFiles/Makefile.cmake 0 /usr/bin/cmake -E cmake_progress_start /home/matrim/workspace/cmake-examples/01-basic/I-compiling-with-clang/build.clang/CMakeFiles /home/matrim/workspace/cmake-examples/01-basic/I-compiling-with-clang/build.clang/CMakeFiles/progress.marks make -f CMakeFiles/Makefile2 all make[1]: Entering directory `/home/matrim/workspace/cmake-examples/01-basic/I-compiling-with-clang/build.clang' make -f CMakeFiles/hello_cmake.dir/build.make CMakeFiles/hello_cmake.dir/depend make[2]: Entering directory `/home/matrim/workspace/cmake-examples/01-basic/I-compiling-with-clang/build.clang' cd /home/matrim/workspace/cmake-examples/01-basic/I-compiling-with-clang/build.clang && /usr/bin/cmake -E cmake_depends "Unix Makefiles" /home/matrim/workspace/cmake-examples/01-basic/I-compiling-with-clang /home/matrim/workspace/cmake-examples/01-basic/I-compiling-with-clang /home/matrim/workspace/cmake-examples/01-basic/I-compiling-with-clang/build.clang /home/matrim/workspace/cmake-examples/01-basic/I-compiling-with-clang/build.clang /home/matrim/workspace/cmake-examples/01-basic/I-compiling-with-clang/build.clang/CMakeFiles/hello_cmake.dir/DependInfo.cmake --color= Dependee "/home/matrim/workspace/cmake-examples/01-basic/I-compiling-with-clang/build.clang/CMakeFiles/hello_cmake.dir/DependInfo.cmake" is newer than depender "/home/matrim/workspace/cmake-examples/01-basic/I-compiling-with-clang/build.clang/CMakeFiles/hello_cmake.dir/depend.internal". Dependee "/home/matrim/workspace/cmake-examples/01-basic/I-compiling-with-clang/build.clang/CMakeFiles/CMakeDirectoryInformation.cmake" is newer than depender "/home/matrim/workspace/cmake-examples/01-basic/I-compiling-with-clang/build.clang/CMakeFiles/hello_cmake.dir/depend.internal". Scanning dependencies of target hello_cmake make[2]: Leaving directory `/home/matrim/workspace/cmake-examples/01-basic/I-compiling-with-clang/build.clang' make -f CMakeFiles/hello_cmake.dir/build.make CMakeFiles/hello_cmake.dir/build make[2]: Entering directory `/home/matrim/workspace/cmake-examples/01-basic/I-compiling-with-clang/build.clang' /usr/bin/cmake -E cmake_progress_report /home/matrim/workspace/cmake-examples/01-basic/I-compiling-with-clang/build.clang/CMakeFiles 1 [100%] Building CXX object CMakeFiles/hello_cmake.dir/main.cpp.o /usr/bin/clang++-3.6 -o CMakeFiles/hello_cmake.dir/main.cpp.o -c /home/matrim/workspace/cmake-examples/01-basic/I-compiling-with-clang/main.cpp Linking CXX executable hello_cmake /usr/bin/cmake -E cmake_link_script CMakeFiles/hello_cmake.dir/link.txt --verbose=1 /usr/bin/clang++-3.6 CMakeFiles/hello_cmake.dir/main.cpp.o -o hello_cmake -rdynamic make[2]: Leaving directory `/home/matrim/workspace/cmake-examples/01-basic/I-compiling-with-clang/build.clang' /usr/bin/cmake -E cmake_progress_report /home/matrim/workspace/cmake-examples/01-basic/I-compiling-with-clang/build.clang/CMakeFiles 1 [100%] Built target hello_cmake make[1]: Leaving directory `/home/matrim/workspace/cmake-examples/01-basic/I-compiling-with-clang/build.clang' /usr/bin/cmake -E cmake_progress_start /home/matrim/workspace/cmake-examples/01-basic/I-compiling-with-clang/build.clang/CMakeFiles 0 $ ./hello_cmake Hello CMake! ----