Shows a hello world example which uses a different folder for source and include files.
The files in this tutorial include:
B-hello-headers$ tree
.
├── CMakeLists.txt
├── include
│ └── Hello.h
└── src
├── Hello.cpp
└── main.cpp-
CMakeLists.txt - Contains the CMake commands you wish to run.
-
include/Hello.h - The header file to include.
-
src/Hello.cpp - A source file to compile.
-
src/main.cpp - The source file with main.
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 directory of the current cmake project. |
CMAKE_BINARY_DIR |
The root binary / build directory. This is the directory where you ran the cmake command. |
CMAKE_CURRENT_BINARY_DIR |
The build directory you are currently in. |
PROJECT_BINARY_DIR |
The build directory for the current project. |
Creating a variable which includes the source files allows you to be clearer about these files and easily add them to multiple commands, for example, the add_executable() function.
# 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})|
Note
|
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") |
|
Tip
|
For modern CMake it is NOT recommended to use a variable for sources. Instead it is typical to directly declare the sources in the add_xxx function. This is particularly important for glob commands which may not always show you the correct results if you add a new source file. |
When you have different include folders, you can make your compiler aware of them using the
target_include_directories() function. When compiling this target this will add these directories to the compiler with the -I flag e.g. -I/directory/path
target_include_directories(target
PRIVATE
${PROJECT_SOURCE_DIR}/include
)The PRIVATE identifier specifies the scope of the include. This is important for libraries and is explained in the next example. More details on the function is available here
The standard output from building this example is presented below.
$ 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!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 flag when running make.
The VERBOSE output is show below, and a examination of the output shows the include directories being added to the c++ compiler 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/include -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/include -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