Hello CMake

Shows a hello world example, which uses a seperate cpp file and include directory.

New Concepts

Directory Paths

CMake syntax specifies a number of variables which can be used to help find useful directories in your project or source tree. Some of these include

Variable	Info
CMAKE_SOURCE_DIR	The root source directory
CMAKE_CURRENT_SOURCE_DIR	The current source directory if using sub-projects and directories
PROJECT_SOURCE_DIR	The source director of the current cmake project.
CMAKE_BINARY_DIR	The root binary / build directory. This is the directory you run the cmake command from
CMAKE_CURRENT_BINARY_DIR	The build directory you are currently in.
PROJECT_BINARY_DIR	The build directory for the current project.

Including Directories

include_directories(
    ${PROJECT_SOURCE_DIR}/inc
    )

When you have a seperate include folders, you can include them using the 'include_directories' function. This will add these directories to the compiler with the -I flag, e.g. -I/directory/path

Setting Source files

# Create a sources variable with a link to all cpp files to compile
set(SOURCES
    src/Hello.cpp
    src/main.cpp
)

add_executable(${PROJECT_NAME} ${SOURCES})

Creating a variable which includes the source files allows you to be clearer about these files and add them to various commands, for example, the 'add_executable()' function.

An alternative to setting specific file names in the SOURCES variable is to use a GLOB command to find files using wildcard pattern matching.

file(GLOB SOURCES "src/*.cpp")

Building the example

$ mkdir build

$ cd build

$ cmake ..
-- The C compiler identification is GNU 4.8.4
-- The CXX compiler identification is GNU 4.8.4
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- 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/hello_headers/build

$ make
Scanning dependencies of target hello_headers
[ 50%] Building CXX object CMakeFiles/hello_headers.dir/src/Hello.cpp.o
[100%] Building CXX object CMakeFiles/hello_headers.dir/src/main.cpp.o
Linking CXX executable hello_headers
[100%] Built target hello_headers

$ ./hello_headers 
Hello Headers!

Verbose Output

In the previous examples, when running the make command the output only shows the status of the build. To see the full output for debugging purposes you can add 'VERBOSE=1' to the command to show all commands.

The VERBOSE output is show below, and looking at the output lets you see the include directories being added to the g++ command.

$ make clean
$ make VERBOSE=1
/usr/bin/cmake -H/home/matrim/workspace/cmake-examples/01-basic/hello_headers -B/home/matrim/workspace/cmake-examples/01-basic/hello_headers/build --check-build-system CMakeFiles/Makefile.cmake 0
/usr/bin/cmake -E cmake_progress_start /home/matrim/workspace/cmake-examples/01-basic/hello_headers/build/CMakeFiles /home/matrim/workspace/cmake-examples/01-basic/hello_headers/build/CMakeFiles/progress.marks
make -f CMakeFiles/Makefile2 all
make[1]: Entering directory `/home/matrim/workspace/cmake-examples/01-basic/hello_headers/build'
make -f CMakeFiles/hello_headers.dir/build.make CMakeFiles/hello_headers.dir/depend
make[2]: Entering directory `/home/matrim/workspace/cmake-examples/01-basic/hello_headers/build'
cd /home/matrim/workspace/cmake-examples/01-basic/hello_headers/build && /usr/bin/cmake -E cmake_depends "Unix Makefiles" /home/matrim/workspace/cmake-examples/01-basic/hello_headers /home/matrim/workspace/cmake-examples/01-basic/hello_headers /home/matrim/workspace/cmake-examples/01-basic/hello_headers/build /home/matrim/workspace/cmake-examples/01-basic/hello_headers/build /home/matrim/workspace/cmake-examples/01-basic/hello_headers/build/CMakeFiles/hello_headers.dir/DependInfo.cmake --color=
make[2]: Leaving directory `/home/matrim/workspace/cmake-examples/01-basic/hello_headers/build'
make -f CMakeFiles/hello_headers.dir/build.make CMakeFiles/hello_headers.dir/build
make[2]: Entering directory `/home/matrim/workspace/cmake-examples/01-basic/hello_headers/build'
/usr/bin/cmake -E cmake_progress_report /home/matrim/workspace/cmake-examples/01-basic/hello_headers/build/CMakeFiles 1
[ 50%] Building CXX object CMakeFiles/hello_headers.dir/src/Hello.cpp.o
/usr/bin/c++    -I/home/matrim/workspace/cmake-examples/01-basic/hello_headers/inc    -o CMakeFiles/hello_headers.dir/src/Hello.cpp.o -c /home/matrim/workspace/cmake-examples/01-basic/hello_headers/src/Hello.cpp
/usr/bin/cmake -E cmake_progress_report /home/matrim/workspace/cmake-examples/01-basic/hello_headers/build/CMakeFiles 2
[100%] Building CXX object CMakeFiles/hello_headers.dir/src/main.cpp.o
/usr/bin/c++    -I/home/matrim/workspace/cmake-examples/01-basic/hello_headers/inc    -o CMakeFiles/hello_headers.dir/src/main.cpp.o -c /home/matrim/workspace/cmake-examples/01-basic/hello_headers/src/main.cpp
Linking CXX executable hello_headers
/usr/bin/cmake -E cmake_link_script CMakeFiles/hello_headers.dir/link.txt --verbose=1
/usr/bin/c++       CMakeFiles/hello_headers.dir/src/Hello.cpp.o CMakeFiles/hello_headers.dir/src/main.cpp.o  -o hello_headers -rdynamic 
make[2]: Leaving directory `/home/matrim/workspace/cmake-examples/01-basic/hello_headers/build'
/usr/bin/cmake -E cmake_progress_report /home/matrim/workspace/cmake-examples/01-basic/hello_headers/build/CMakeFiles  1 2
[100%] Built target hello_headers
make[1]: Leaving directory `/home/matrim/workspace/cmake-examples/01-basic/hello_headers/build'
/usr/bin/cmake -E cmake_progress_start /home/matrim/workspace/cmake-examples/01-basic/hello_headers/build/CMakeFiles 0

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