CMake - "Hello world"

Definition from Wikipedia

In software development, CMake is cross-platform free and open-source software for build automation, testing, packaging and installation of software by using a compiler-independent method.

So, clearly, CMake is not a build system but rather it generates another system's build files.

Source code

Lets have a simple mainapp.cpp that will flush to output the string "Hello world!"

#include<stdio.h>​
// ----------------------------------​
// Greeting message in English​
// ----------------------------------​
void  greeting_en()​
{​
    printf("Hello world!\n");​
}​      ​
// ----------------------------------​
// Main functions​
// ----------------------------------​
int  main(int  argc, char* argv[])​
{​
    greeting_en();​
    return 0;​
}

CMakeLists

CMakeLists.txt that is put in the same level with mainapp.cpp with content:

# -------------------------------------------​
# The minimum version that required to be able to read this CMakeList.txt​
# -------------------------------------------​
cmake_minimum_required(VERSION 2.8.12)​
​
# -------------------------------------------​
# Project name often named as the binary (executable) file​
# -------------------------------------------​
project(helloworld)​
​
# -------------------------------------------​
# Define the relationship between the the source code and the binary file​
# -------------------------------------------​
add_executable(helloworld mainapp.cpp)

Putting the two files into the same directory, the hierarchy file can be seen by command tree as

root@ubuntu-22:/home/henry/HENRY_LAB/How_to_write_CMake/cmake_practice_01_single_source_code# tree
.
├── CMakeLists.txt
└── mainapp.cpp

The file CMakeList.txt acts like a definition that CMake could understand, here we goes into the project before running the following command:

[root@base06 cmake_practice_01_single_source_code]# cmake .​

Note: The dot "." is very important, it is the navigator to the path that store the file CMakeList.txt. In this case we can change it to $(PWD), the result should be the same.​

Build the code

root@ubuntu-22:/home/henry/HENRY_LAB/How_to_write_CMake/cmake_practice_01_single_source_code# cmake .
-- The C compiler identification is GNU 11.2.0
-- The CXX compiler identification is GNU 11.2.0
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: /home/henry/HENRY_LAB/How_to_write_CMake/cmake_practice_01_single_source_code

As we can see, there are many files and folder created during the running of CMake. In this tutorial, we only focus on the Makefile created

Observe:​

• CMake's duty is helping to generate Makefile, in other words, it is NOT helping us to build the project but to generate the Makefile only and then . . . done!​
• As Wikipedia defines, CMake is NOT a build system.

So now, to build the project, we invoke Makefiles with command make​​

root@ubuntu-22:/home/henry/HENRY_LAB/How_to_write_CMake/cmake_practice_01_single_source_code# make
[ 50%] Building CXX object CMakeFiles/helloworld.dir/mainapp.cpp.o
[100%] Linking CXX executable helloworld
[100%] Built target helloworld

The result will be an executable file named helloworld as below​

root@ubuntu-22:/home/henry/HENRY_LAB/How_to_write_CMake/cmake_practice_01_single_source_code# ls -la
total 64
drwxrwxr-x  3 henry henry  4096  八  31 21:56 .
drwxrwxr-x 10 henry henry  4096  八  31 20:49 ..
-rw-r--r--  1 root  root  14018  八  31 21:50 CMakeCache.txt
drwxr-xr-x  5 root  root   4096  八  31 21:56 CMakeFiles
-rw-r--r--  1 root  root   1724  八  31 21:50 cmake_install.cmake
-rw-rw-r--  1 henry henry   583  六   9 10:13 CMakeLists.txt
-rwxr-xr-x  1 root  root  16000  八  31 21:56 helloworld
-rw-rw-r--  1 henry henry   351  六   9 10:08 mainapp.cpp
-rw-r--r--  1 root  root   5467  八  31 21:50 Makefile

Enjoy the result

Execute the file, we see the expected result:​

root@ubuntu-22:/home/henry/HENRY_LAB/How_to_write_CMake/cmake_practice_01_single_source_code# ./helloworld
Hello world!

Source code can be found here

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