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