cmake_minimum_required(VERSION 3.14...3.18)
project(MyProject
  VERSION 1.0
  DESCRIPTION "Very nice project"
  LANGUAGES CXX)
add_executable(myexample simple.cpp)

set(MY_VARIABLE "I am a variable")
set(MY_CACHE_VAR "I am a cached variable" CACHE STRING "Description")

# 下面两句等价
option(MY_OPTION "On or off" OFF) 
set(MY_OPTION OFF CACHE BOOL "On or off")

# 可执行文件
add_executable(<name> [source1] [source2 ...])

# 例子：
add_library(archive archive.cpp zip.cpp lzma.cpp)
add_executable(zipapp zipapp.cpp)
target_link_libraries(zipapp archive)

# Normal Lib（静态 vs. 动态）
add_library(<name> [STATIC | SHARED | MODULE]
            [EXCLUDE_FROM_ALL]
            [<source>...])
            
# 例子：静态库
add_library(archive STATIC archive.cpp zip.cpp lzma.cpp)
# 例子：动态库
add_library(archive SHARED archive.cpp zip.cpp lzma.cpp)

##############
# Object Lib（目标文件库，不生成archive文件）
add_library(<name> OBJECT [<source>...])

# 例子：作为obj文件集合被引用
add_library(archive OBJECT archive.cpp zip.cpp lzma.cpp)
add_library(archiveExtras STATIC $<TARGET_OBJECTS:archive> extras.cpp)
add_executable(test_exe $<TARGET_OBJECTS:archive> test.cpp)

# 例子：可以被链接到其它target
add_library(archive OBJECT archive.cpp zip.cpp lzma.cpp)

add_library(archiveExtras STATIC extras.cpp)
target_link_libraries(archiveExtras PUBLIC archive)

add_executable(test_exe test.cpp)
target_link_libraries(test_exe archive)

##############
# Interface Lib（接口库，不进行编译和生成archive文件，主要用于header-only的库）
add_library(<name> INTERFACE)

# 例子：
add_library(Eigen INTERFACE
  src/eigen.h
  src/vector.h
  src/matrix.h
  )
target_include_directories(Eigen INTERFACE
  $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/src>
  $<INSTALL_INTERFACE:include/Eigen>
)

add_executable(exe1 exe1.cpp)
target_link_libraries(exe1 Eigen)

##############
# Imported Lib（导入的库，外部构建好的库）
add_library(<name> <STATIC/SHARED/MODULE/UNKNOWN/OBJECT/INTERFACE> IMPORTED [GLOBAL])

##############
# Alias Target（Target别名，不能install和export）
add_library(<name> ALIAS <target>)

# TARGET-ORIENTED NEW COMMANDS

# 链接依赖
target_link_libraries(<target> [VISIBILITY] ... <item>... ...)
# 包含路径
target_include_directories(<target> [VISIBILITY] <include_path>)

# 预编译定义
target_compile_definitions(<target> [VISIBILITY] <preprocessor_flags>)
# 编译器选项
target_compile_options(<target> [VISIBILITY] <compilation_flags>)
# 编译器特性支持
target_compile_features(<target> [VISIBILITY]> <feature>)
# 链接选项
target_link_options(<target> [VISIBILITY] <linker_flags>)
# 指定链接目录（不建议使用）
target_link_directories(<target> [VISIBILITY] <link_path) 

# DIRECTORY-ORIENTED OLD COMMANDS（Deprecated）
include_directories(<include_path>)	
add_definitions(<preprocessor_flags>)	
set(CMAKE_CXX_FLAGS <compilation_flags>)
set(CMAKE_LINKER_FLAGS <linker_flags>)	

INCLUDE( FindPackageHandleStandardArgs )

# Checks an environment variable; note that the first check
# does not require the usual CMake $-sign.
IF( DEFINED ENV{FOO_DIR} )
  SET( FOO_DIR "$ENV{FOO_DIR}" )
ENDIF()

FIND_PATH(
  FOO_INCLUDE_DIR
    foo/foo.h
  HINTS
    ${FOO_DIR}
)

FIND_PACKAGE_HANDLE_STANDARD_ARGS( FOO DEFAULT_MSG
  FOO_INCLUDE_DIR
)

IF( FOO_FOUND )
  SET( FOO_INCLUDE_DIRS ${FOO_INCLUDE_DIR} )

  MARK_AS_ADVANCED(
    FOO_INCLUDE_DIR
    FOO_DIR
  )
ELSE()
  SET( FOO_DIR "" CACHE STRING
    "An optional hint to a directory for finding `foo`"
  )
ENDIF()

LIST( APPEND CMAKE_MODULE_PATH
  ${CMAKE_SOURCE_DIR}/cmake/Modules
)

FIND_PACKAGE( foo REQUIRED )
TARGET_INCLUDE_DIRECTORIES( example ${FOO_INCLUDE_DIRS} )

# FindBar.cmake
#
INCLUDE( FindPackageHandleStandardArgs )

# Checks an environment variable; note that the first check
# does not require the usual CMake $-sign.
IF( DEFINED ENV{BAR_DIR} )
  SET( BAR_DIR "$ENV{BAR_DIR}" )
ENDIF()

FIND_PATH(
  BAR_INCLUDE_DIR
    bar/bar.h
  HINTS
    ${BAR_DIR}
)

FIND_LIBRARY( BAR_LIBRARY
  NAMES bar
  HINTS ${BAR_DIR}
)

FIND_PACKAGE_HANDLE_STANDARD_ARGS( BAR DEFAULT_MSG
  BAR_INCLUDE_DIR
  BAR_LIBRARY
)

IF( BAR_FOUND )
  SET( BAR_INCLUDE_DIRS ${BAR_INCLUDE_DIR} )
  SET( BAR_LIBRARIES ${BAR_LIBRARY} )

  MARK_AS_ADVANCED(
    BAR_LIBRARY
    BAR_INCLUDE_DIR
    BAR_DIR
  )
ELSE()
  SET( BAR_DIR "" CACHE STRING
    "An optional hint to a directory for finding `bar`"
  )
ENDIF()

# CMakeListst.txt
TARGET_LINK_LIBRARIES( example ${BAR_LIBRARIES} )

IF( CMAKE_CXX_COMPILER_VERSION VERSION_LESS "5.4.1" )
  MESSAGE( STATUS "This compiler version might cause problems" )
ENDIF()

IF( APPLE )
  MESSAGE( STATUS "Running under MacOS X" )
# Watch out, for this check also is TRUE under MacOS X because it
# falls under the category of Unix-like.
ELSEIF( UNIX )
  MESSAGE( STATUS "Running under Unix or a Unix-like OS" )
# Despite what you might think given this name, the variable is also
# true for 64bit versions of Windows.
ELSEIF( WIN32 )
  MESSAGE( STATUS "Running under Windows (either 32bit or 64bit)" )
ENDIF()

IF( CMAKE_CXX_COMPILER_ID MATCHES "GNU" )
  MESSAGE( STATUS "g++ for the win!" )
  MESSAGE( STATUS ${CMAKE_CXX_COMPILER_VERSION} )
ENDIF()

IF( CMAKE_CXX_COMPILER_ID MATCHES "Clang" )
  MESSAGE( STATUS "LLVM, yeah!" )
ENDIF()

SET( CMAKE_CXX_STANDARD 11 )
SET( CMAKE_CXX_STANDARD_REQUIRED ON )