# Learning CMake: A beginner's guide

## 1. What is CMake?

From the CMake’s website:

CMake is an extensible, open-source system that manages the build process in an operating system and in a compiler-independent manner. Unlike many cross-platform systems, CMake is designed to be used in conjunction with the native build environment. Simple configuration files placed in each source directory (called CMakeLists.txt files) are used to generate standard build files (e.g., makefiles on Unix and projects/workspaces in Windows MSVC) which are used in the usual way. CMake can generate a native build environment that will compile source code, create libraries, generate wrappers and build executables in arbitrary combinations. CMake supports in-place and out-of-place builds, and can therefore support multiple builds from a single source tree. CMake also supports static and dynamic library builds. Another nice feature of CMake is that it generates a cache file that is designed to be used with a graphical editor. For example, when CMake runs, it locates include files, libraries, and executables, and may encounter optional build directives. This information is gathered into the cache, which may be changed by the user prior to the generation of the native build files.

In a short conclusion, CMake help you to manage and build your source codes effectively. If you have some troubles with gcc and Makefile, just move out to CMake.

## 2. Installation

To install CMake in Linux, just simply do on your terminal

# For Ubuntu

$sudo apt-get install cmake # For Redhat$ yum install cmake

# For Mac OS X with Macports

$sudo port install cmake  ## 3. Quick start So I assume that you know C++ and what the Makefile is. CMake will do the job of Makefile from now. Let start with a simple C++ program. // test.cpp #include <iostream> using namespace std; int main(void) { cout << "Hello World" << endl; return(0); }  And you saved it as test.cpp, then to compile it in CMake you should create a txt file named CMakeLists.txt # Specify the minimum version for CMake cmake_minimum_required(VERSION 2.8) # Project's name project(hello) # Set the output folder where your program will be created set(CMAKE_BINARY_DIR${CMAKE_SOURCE_DIR}/bin)
set(EXECUTABLE_OUTPUT_PATH ${CMAKE_BINARY_DIR}) set(LIBRARY_OUTPUT_PATH${CMAKE_BINARY_DIR})

# The following folder will be included
include_directories("${PROJECT_SOURCE_DIR}")  There is a list of CMake’s global varibales. You should know them. CMAKE_BINARY_DIR if you are building in-source, this is the same as CMAKE_SOURCE_DIR, otherwise this is the top level directory of your build tree CMAKE_SOURCE_DIR this is the directory, from which cmake was started, i.e. the top level source directory EXECUTABLE_OUTPUT_PATH set this variable to specify a common place where CMake should put all executable files (instead of CMAKE_CURRENT_BINARY_DIR) SET(EXECUTABLE_OUTPUT_PATH${PROJECT_BINARY_DIR}/bin)


LIBRARY_OUTPUT_PATH

set this variable to specify a common place where CMake should put all libraries (instead of CMAKE_CURRENT_BINARY_DIR)

SET(LIBRARY_OUTPUT_PATH ${PROJECT_BINARY_DIR}/lib)  PROJECT_NAME the name of the project set by PROJECT() command. PROJECT_SOURCE_DIR contains the full path to the root of your project source directory, i.e. to the nearest directory where CMakeLists.txt contains the PROJECT() command Now, you have to compile the test.cpp. The way to do this task is too simple. Add the following line into your CMakeLists.txt: add_executable(hello${PROJECT_SOURCE_DIR}/test.cpp)


Now, let build the source code with CMake. At this point, you will have the folder with the following files:

$ls test.cpp CMakeLists.txt  To build your project hello, just do $ cmake -H. -Bbuild
$cmake --build build -- -j3  The first command will creates CMake configuration files inside folder build and the second one will generate the output program hello in bin folder. You should test your output: $ ./bin/hello
Hello World


Too simple, right?

The source code of this sample project canbe found at CMakeLists.txt and test.cpp