Cmake tutorial series -04- compiling related functions

1. introduce

The compilation process and the linking process need to Compiler and linker Pass in different parameters , These parameters fall into the following categories ：

• Compilation options （ Including macro definitions ）
• Header file path
• Link library file name
• Link library lookup path

2.target_compile_options

This function adds compilation options to the target ,

• Its prototype is ：

target_compile_options(<target> [BEFORE]
  <INTERFACE|PUBLIC|PRIVATE> [items1...]
  [<INTERFACE|PUBLIC|PRIVATE> [items2...] ...])

• eg：

target_compile_options(sample PUBLIC /arch=avx2 /Wall)

It should be noted that , If you want to set c / c++ standard , Not only can you use this function to add -std=STANDARD, It is also possible and more recommended to set the following two cmake Preset macro values ：

• Just fill in the number of the standard number ,cmake Standard related options will be automatically set .

CMAKE_C_STANDARD
CMAKE_CXX_STANDARD

2.target_compile_definitions

This function adds a preset macro declaration and definition to the target .

• Of course , You can also use the above function to do this , After all, the parameters in the command line are not ？
• But professional people do professional things , It is recommended to use this function to add macro definitions . Its prototype is ：

target_compile_definitions(<target>
  <INTERFACE|PUBLIC|PRIVATE> [items1...]
  [<INTERFACE|PUBLIC|PRIVATE> [items2...] ...])

• eg：

target_compile_definitions(sample PRIVATE BUILD_DLL PUBLIC "-DPI=3.14159")

3.target_compile_features

This function sets... Specifically to the target c / c++ edition . Of course , You can still choose between the two approaches in the first function .

• Its prototype is ：

target_compile_features(<target> <PRIVATE|PUBLIC|INTERFACE> <feature> [...])

• for example ：

target_compile_features(sample PUBLIC cxx_std_17)

4.target_precompile_headers

This function adds a precompiled header file to the target .

• Is the use of Visual Studio Automatically created after creating a new project pch.h This kind of document .
• Its prototype is ：

target_precompile_headers(<target>
  <INTERFACE|PUBLIC|PRIVATE> [header1...]
  [<INTERFACE|PUBLIC|PRIVATE> [header2...] ...])

• eg：

target_precompile_headers(sample PRIVATE pch.hpp)

5.target_include_directories

This function declares the path to use the header file when compiling the target .

• Its prototype is ：

target_include_directories(<target> [SYSTEM] [AFTER|BEFORE]
  <INTERFACE|PUBLIC|PRIVATE> [items1...]
  [<INTERFACE|PUBLIC|PRIVATE> [items2...] ...])

• eg：

target_include_directories(sample PUBLIC public/include/sample PRIVATE sample)

6.target_link_libraries

This function declares the name of the dependent library or target. Its name can contain the full path .

• Its prototype is ：

target_link_libraries(<target>
  <INTERFACE|PUBLIC|PRIVATE> [items1...]
  [<INTERFACE|PUBLIC|PRIVATE> [items2...] ...])

• eg：

target_link_libraries(sample PUBLIC CURL::curl glib m)

Be careful ： Due to a target Contains multiple attributes , Generally, the header file path is included .

• So use target When this function is passed as an argument , Don't need to call target_include_directories Once again, add the header file path .

7.target_link_directories

This function declares When linking , Find the path to the dependent library .

• Its prototype is ：

target_link_directories(<target> [BEFORE]
  <INTERFACE|PUBLIC|PRIVATE> [items1...]
  [<INTERFACE|PUBLIC|PRIVATE> [items2...] ...])

• eg：

target_link_directories(sample PUBLIC third_party/libs/x86/rel)

8.target_link_options

This function declares the option to add additional links .

• Its prototype is ：

target_link_options(<target> [BEFORE]
  <INTERFACE|PUBLIC|PRIVATE> [items1...]
  [<INTERFACE|PUBLIC|PRIVATE> [items2...] ...])

• eg：

target_link_options(sample PUBLIC /shared)

9.target_sources

This function declares to target Add source file .

• Its prototype is ：

target_sources(<target>
  <INTERFACE|PUBLIC|PRIVATE> [items1...]
  [<INTERFACE|PUBLIC|PRIVATE> [items2...] ...])

• eg：

target_sources(sample PRIVATE decode.cxx)

notes ： Don't think this function is completely useless , Can be add_library / add_executable replace . In some cases , This function is very easy to use .

• eg：
  I need to provide a library containing only source code for downstream use , Instead of compiling the binary and providing it to the downstream . here , We need to use add_library(sample INTERFACE) And use this function to add a source file to link to sample , And pass cmake Export this target. In this way , Downstream only need to use target Family functions can use the source files provided by me without any additional code .

10.target Family function considerations

When needed cmake export Keyword export declared target With the PUBLIC Attribute , We have to take PUBLIC / PRIVATE / INTERFACE Keyword to this kind of target Family function complement . And if one target Family functions declare one of these three keywords , The target Other target All family functions should declare keywords . And for values that contain paths , We need to declare the scope of this value ：

• compile / Use when linking . Absolute path must be used .
• Export to provide... Downstream . Relative paths must be used .

therefore , We usually use the following methods ：

target_include_directories(sample PRIVATE $<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}/header/include> PUBLIC $<INSTALL_INTERFACE:include>)

11. Complete example

cmake_minimum_required(VERSION 3.0)
project(sample CXX)
set(CMAKE_CXX_STANDARD 11)

add_library(sample sample.cpp)
target_include_directories(sample PRIVATE $<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}/header/include> PUBLIC $<INSTALL_INTERFACE:include>)
target_compile_options(sample PUBLIC /Wall)
target_compile_definitions(sample PRIVATE BUILD_DLL INTERFACE USE_DLL)
target_link_libraries(sample PRIVATE thread m)

• Reference resources ：CMake Tutorial series -04- Compile related functions