《Modern CMake》读书笔记

1. Running cmake

1.1. cmake选项

--build  指定输出目录

-j 指定并行度

--target 指定编译目标

1.2. 选择编译器

EXPORT CC=clang CXX=clang++ cmake ..

1.3. 选择生成器

默认为make  通过cmake -G Ninja指定ninja

1.4. 指定编译选项

cmake -DXXX=YYY

cmake会将各种编译选项缓存到一个文件中，即CMakeCache.txt

1.5. 调试

调试makefile: VERBOSE=1 make

调试cmake:

• cmake --trace,  打印出cmake运行的每一行脚本

• cmake --trace-source=打印出中运行的每一行脚本

1.6. 指定编译类型

-DCMAKE_BUILD_TYPE：Debug或Release或RelWithDebInfo

-DCMAKE_INSTALL_PREFIX: 指定安装路径，默认为/usr/local

-DBUILD_SHARED_LIBS: 是否编译共享库，ON or OFF

-DBUILD_TESTING:  是否编译tests

2. Do's and Don'ts

2.1. 不要做

• 不要使用全局函数:  link_directories, include_libraries等

• 非必要不使用PULIBC限制

• 不要用glob匹配文件：当新增文件时，除非重新跑一遍cmake, make或其他编译工具将不会感知到新文件

• lib不要直接link到最终的target

• link lib时不要忽略PUBLIC/PRIVATE关键字

2.2. 要做

• 把cmake当做正经代码维护

• 站在target的角度思考

• 善用alias

• 将通用功能抽象成函数或宏

• 函数名统一小写

• 善用cmake_policy

2.3. 选择cmake版本

2.3.1. os支持

• 3.4: The bare minimum. Never set less.

• 3.7: Debian old-stable.

• 3.10: Ubuntu 18.04.

• 3.11: CentOS 8 (use EPEL or AppSteams, though)

• 3.13: Debian stable.

• 3.16: Ubuntu 20.04.

• 3.19: First to support Apple Silicon.

• latest: pip/conda-forge/homebew/chocolaty, ect.

笔者目前用的是3.16

2.3.2. 特性

• 3.8: C++ meta features, CUDA, lots more

• 3.11: IMPORTED INTERFACE setting, faster, FetchContent, COMPILE_LANGUAGE in IDEs

• 3.12: C++20, cmake --build build -j N, SHELL:, FindPython

• 3.14/3.15: CLI, FindPython updates

• 3.16: Unity builds / precompiled headers, CUDA meta features

• 3.17/3.18: Lots more CUDA, metaprogramming

3. What's new in in CMake

• cmake 3.0: interface libraries, 允许将一组头文件抽象成一个lib

• cmake 3.1: 支持c++11和compile features

• cmake 3.2: 支持UTF-8

• cmake 3.4:  支持swift语言，支持ccache

• cmake 3.5: 支持ARM平台

• cmake 3.6: 支持clang-tidy

• 其他：略
• 
  

4. 基础知识

指定最小版本

cmake_minimum_required(VERSION 3.1)

创建工程

project(MyProject VERSION 1.0
                  DESCRIPTION "Very nice project"
                  LANGUAGES CXX)

新增executable

add_executable(one two.cpp three.h)

新增library

add_library(one STATIC two.cpp three.h)

用户可指定STATIC、SHARED、MODULE 。缺省使用BUILD_SHARED_LIBS选项。

INTERFAC用于创建头文件库

ALIAS用于指定库的别名.

绑定头文件路径

target_include_directories(one PUBLIC include)

PUBLIC表示所有依赖lib的target都自动绑定了该头文件路径

PRIVATE表示该头文件路径仅对本target有效

INTERFACE表示该头文件路径仅对依赖该lib的target生效

PUBLIC = PRIVATE + INTERFACE

5. 变量和cache

定义变量

set(MY_VARIABLE "value")

访问变量时使用${MY_VARIABLE}

变量仅在当前作用域内有效。

定义变量(多个值)

set(MY_LIST "one" "two")

等效于

set(MY_LIST "one;two")

属性

set_property(TARGET TargetName
             PROPERTY CXX_STANDARD 11)
set_target_properties(TargetName PROPERTIES
                      CXX_STANDARD 11)
get_property(ResultVariable TARGET TargetName PROPERTY CXX_STANDARD)

6. cmake编程

6.1. 控制流

if(variable)
    # If variable is `ON`, `YES`, `TRUE`, `Y`, or non zero number
else()
    # If variable is `0`, `OFF`, `NO`, `FALSE`, `N`, `IGNORE`, `NOTFOUND`, `""`, or ends in `-NOTFOUND`
endif()
# If variable does not expand to one of the above, CMake will expand it then try again

There are a variety of keywords as well, such as:

• Unary: NOT, TARGET, EXISTS (file), DEFINED, etc.
  
• Binary: STREQUAL, AND, OR, MATCHES (regular expression), VERSION_LESS, VERSION_LESS_EQUAL (CMake 3.7+), etc.
  
• Parentheses can be used to group

generator-expressions

target_compile_options(MyTarget PRIVATE "$<$<CONFIG:Debug>:--my-flag>")

当使用debug编译时，加上--my-flag编译选项

That last one is very common. You'll see something like this in almost every package that supports installing:

target_include_directories(
    MyTarget
  PUBLIC
    $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
    $<INSTALL_INTERFACE:include>
)