Tool Linux

CMake Introduction

Introduction

CMake is an open-source, cross-platform software development tool for creating, testing, and packaging software. It is used to manage the build process of a software project, including generating the necessary Makefiles and other build files.

CMake is a meta-build system, which means that it does not directly generate the build files for a project. Instead, it generates scripts that are used by other build systems, such as Make or Ninja. This makes CMake portable and flexible, as it can be used with different build systems on different platforms.

CMake is written in the C++ programming language, but it can be used to build projects written in any programming language. It is a popular choice for building software projects, as it is easy to use and provides a high level of control over the build process.

param

The CMake command-line options are used to control the behavior of the CMake tool. Here are some of the most commonly used options:

  • -G: This option specifies the build system that should be used. For example, -G Ninja specifies that Ninja should be used as the build system.
  • -D: This option defines a CMake variable. For example, -DCMAKE_BUILD_TYPE=Release defines the build type as Release.
  • -S: This option specifies the source directory. For example, -S /path/to/source specifies that the source directory is /path/to/source.
  • -B: This option specifies the build directory. For example, -B /path/to/build specifies that the build directory is /path/to/build.
  • -W: This option specifies a warning option. For example, -Werror specifies that all warnings should be treated as errors.
  • -v: This option prints verbose output.

For a complete list of CMake command-line options, please refer to the CMake documentation: https://cmake.org/cmake/help/latest/manual/cmake.1.html.

Here are some examples of how to use the CMake command-line options:

  • To build a project using Ninja as the build system:
cmake -G Ninja .
  • To define the build type as Release:
cmake -DCMAKE_BUILD_TYPE=Release .
  • To specify the source directory as /path/to/source:
cmake -S /path/to/source .
  • To specify the build directory as /path/to/build:
cmake -B /path/to/build .
  • To print verbose output:
cmake -v .

output

CMake supports a variety of build systems, including:

  • Make
  • Ninja
  • Watcom WMake
  • MSVC
  • Xcode
  • Code::Blocks
  • Eclipse CDT
  • KDevelop
  • Qt Creator
  • Android Studio
  • Visual Studio Code

CMake can also be used to generate build files for other build systems, such as:

  • SCons
  • Bazel
  • Meson

The specific build system that is used depends on the project and the preferences of the developer.

Here are some of the factors that can affect the choice of build system:

  • The platform that the project is being built on.
  • The programming language that the project is written in.
  • The size and complexity of the project.
  • The preferences of the developer.

CMake is a powerful tool that can be used to build software projects on different platforms. It is well-documented and there are many resources available to help users learn how to use it. However, it can be complex to learn and use, especially for complex projects.

grammar

The CMake grammar is the set of rules that define how CMake scripts are written. The CMake grammar is based on the C++ programming language, but it is simplified and has its own syntax.

The basic building block of a CMake script is a statement. A statement is a command that tells CMake to do something. Statements are terminated by a semicolon (;).

Here are some examples of CMake statements:

cmake_minimum_required(VERSION 3.10)
project(my_project)
add_executable(my_executable main.cpp)

The cmake_minimum_required statement tells CMake that the project requires at least CMake version 3.10. The project statement defines the name of the project. The add_executable statement creates an executable target named my_executable that is built from the main.cpp file.

CMake scripts can also contain comments. Comments are ignored by CMake.

Here is an example of a comment:

# This is a comment.

CMake scripts can also contain variables. Variables are used to store values that can be used by CMake scripts.

Here is an example of a variable:

set(CMAKE_CXX_FLAGS "-Wall -Wextra -Werror")

The set function is used to set the value of a variable. In this case, the CMAKE_CXX_FLAGS variable is set to a list of compiler flags.

Here are the steps on how to define a function and how to use message to print error and info in CMake file:

  1. Define a function using the function keyword. The syntax for the function keyword is:
function(<function_name> <arguments>)

The <function_name> argument is the name of the function. The <arguments> argument is a list of the arguments that the function takes.

  1. Define the body of the function. The body of the function is a block of statements that are executed when the function is called.

  2. End the function definition with the endfunction keyword.

Here is an example of a function that prints the message “Hello, world!” to the console:

function(hello_world)
  message(STATUS "Hello, world!")
endfunction()

To call the function, you can use the call function. The syntax for the call function is:

call(<function_name> <arguments>)

The <function_name> argument is the name of the function that you want to call. The <arguments> argument is a list of the arguments that you want to pass to the function.

Here is an example of how to call the hello_world function:

call(hello_world)

To print an error message, you can use the message function with the FATAL_ERROR keyword. The syntax for the message function with the FATAL_ERROR keyword is:

message(FATAL_ERROR <message>)

The <message> argument is the message that you want to print.

Here is an example of how to print an error message:

message(FATAL_ERROR "This is an error message!")

To print an information message, you can use the message function with the STATUS keyword. The syntax for the message function with the STATUS keyword is:

message(STATUS <message>)

The <message> argument is the message that you want to print.

Here is an example of how to print an information message:

message(STATUS "This is an information message!")

For more information on the CMake grammar, please refer to the CMake documentation: https://cmake.org/cmake/help/latest/manual/cmake.1.html.

target

CMake predefined rules are a set of rules that are automatically defined by CMake. These rules can be used to create common targets, such as executables, libraries, and tests.

To use a predefined rule, you need to call the corresponding function. For example, to create an executable target, you would call the add_executable function.

Here is a list of some of the most commonly used CMake predefined rules:

  • add_executable: This function is used to create an executable target.
  • add_library: This function is used to create a library target.
  • add_test: This function is used to create a test target.
  • install: This function is used to install targets to a specific location.
  • target_link_libraries: This function is used to link targets together.
  • target_compile_options: This function is used to set the compiler options for a target.

For more information on CMake predefined rules, please refer to the CMake documentation: https://cmake.org/cmake/help/latest/manual/cmake.1.html.

Here is an example of how to use the add_executable function to create an executable target named my_executable that is built from the main.cpp file:

add_executable(my_executable main.cpp)

lib

CMake has a few files that can be used to help find shared libraries and related flags.

  • The CMakeLists.txt file: This is the main CMake file for a project. It is used to define the project’s settings and targets.
  • The FindXXX.cmake files: These files are used to find libraries and other dependencies. There are many different FindXXX.cmake files, each for a different library or dependency.
  • The toolchain.cmake file: This file is used to define the toolchain for a project. The toolchain is the set of tools that are used to build the project.

The CMakeLists.txt file is the most important file for finding shared libraries. It can be used to specify the location of the shared libraries, as well as the compiler flags that are needed to link to them.

The FindXXX.cmake files can be used to find shared libraries that are not installed in a standard location. These files typically use the find_library function to search for the library.

The toolchain.cmake file can be used to define the compiler and linker flags that are used to build the project. This can be useful if the project needs to be built with a specific set of compiler flags.

Summary

Here are some of the benefits of using CMake:

  • It is cross-platform: CMake can be used to build software projects on different platforms, including Linux, macOS, Windows, and others.
  • It is portable: CMake scripts are portable and can be used to build software projects on different systems.
  • It is flexible: CMake can be used with different build systems, such as Make or Ninja.
  • It is powerful: CMake provides a high level of control over the build process.
  • It is well-documented: CMake is well-documented and there are many resources available to help users learn how to use it.

Here are some of the limitations of using CMake:

  • It can be complex: CMake can be complex to learn and use, especially for complex projects.
  • It can be slow: CMake can be slow to generate the build files for large projects.
  • It can be inflexible: CMake can be inflexible in some cases, such as when trying to integrate with existing build systems.

Overall, CMake is a powerful and flexible tool that can be used to build software projects on different platforms. It is well-documented and there are many resources available to help users learn how to use it. However, it can be complex to learn and use, especially for complex projects.