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target_include_directories
命令格式
target_include_directories(<target> [SYSTEM] [AFTER|BEFORE]
<INTERFACE|PUBLIC|PRIVATE> [items1...]
[<INTERFACE|PUBLIC|PRIVATE> [items2...] ...])该命令给指定的目标文件添加头文件搜索目录，所以<target>必须用add_executable()或add_library()等命令先创建出来，和include_directories的主要差别是：
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include_directories会对当前CMakeLists.txt文件的目标文件生效，并会通过add_subdirectory调用传递到子目录；target_include_directories则针对指定的目标文件生效。
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target_include_directories对于指定目标添加的目录，有三种范围可选，PUBLIC、PRIVATE和INTERFACE。INTERFACE和PUBLIC会添加到<target>的INTERFACE_INCLUDE_DIRECTORIES属性，PUBLIC和PRIVATE会添加到<target>的INCLUDE_DIRECTORIES属性中。
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参数选项
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AFTER或BEFORE
指定添加的目录是追加到头文件搜索目录列表，还是在头文件搜索目录列表的最前面插入。
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SYSTEM
该选项表明被添加的目录是系统目录，系统目录的搜索顺序在普通的头文件搜索目录之后，并且会添加到目标的INTERFACE_SYSTEM_INCLUDE_DIRECTORIES属性中。
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INTERFACE或PUBLIC或PRIVATE
指定添加到目标的范围属性，INTERFACE和PUBLIC会添加到<target>的INTERFACE_INCLUDE_DIRECTORIES属性，PUBLIC和PRIVATE会添加到<target>的INCLUDE_DIRECTORIES属性中。
示例说明
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为可执行文件添加头文件搜索目录
目录结构
target_include_directories/ ├── CMakeLists.txt └── main.cppCMakeLists.txt文件内容：
cmake_minimum_required(VERSION 3.22) project(target_include_test) add_executable(main main.cpp) target_include_directories(main PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}) get_property(dirs_interface TARGET main PROPERTY INTERFACE_INCLUDE_DIRECTORIES) get_property(dirs_normal TARGET main PROPERTY INCLUDE_DIRECTORIES) message("# In parent scope, target main: interface[${dirs_interface}], normal[${dirs_normal}]")main.cpp文件内容：
#include <iostream> int main(int argc, char** argv) { std::cout << "In main..." << std::endl; return 0; }在target_include_directories目录下，运行
cmake .以及make VERBOSE=1，关键输出：$ cmake . …… # In parent scope, target main: interface[], normal[/XXX/target_include_directories] $ make VERBOSE=1 …… /usr/bin/c++ -MD -MT CMakeFiles/main.dir/main.cpp.o -MF CMakeFiles/main.dir/main.cpp.o.d -o CMakeFiles/main.dir/main.cpp.o -c /XXX/target_include_directories/main.cpp $ ./main In main...
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头文件目录的传递性
目录结构：
其中test编译为库文件，提供了一个test_print()的函数。
target_include_directories/ ├── CMakeLists.txt ├── main.cpp └── test ├── CMakeLists.txt ├── test.cpp └── test.h1）可执行文件main不添加test目录，库文件编译时添加INTERFACE范围的test目录
target_include_directories/CMakeLists.txt文件内容：
cmake_minimum_required(VERSION 3.22) project(target_include_test) add_subdirectory(test) add_executable(main main.cpp) get_property(dirs_interface TARGET main PROPERTY INTERFACE_INCLUDE_DIRECTORIES) get_property(dirs_normal TARGET main PROPERTY INCLUDE_DIRECTORIES) message("# In parent scope, target main property: interface[${dirs_interface}], normal[${dirs_normal}]") target_link_libraries(main test) get_property(dirs_interface TARGET main PROPERTY INTERFACE_INCLUDE_DIRECTORIES) get_property(dirs_normal TARGET main PROPERTY INCLUDE_DIRECTORIES) message("# In parent scope, after add test lib, target main property: interface[${dirs_interface}], normal[${dirs_normal}]")target_include_directories/main.cpp文件内容：
#include "test.h" #include <iostream> int main(int argc, char** argv) { std::cout << "In main..." << std::endl; test_print(); return 0; }target_include_directories/test/CMakeLists.txt文件内容：
add_library(test test.cpp) target_include_directories(test INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}) get_property(dirs_interface TARGET test PROPERTY INTERFACE_INCLUDE_DIRECTORIES) get_property(dirs_normal TARGET test PROPERTY INCLUDE_DIRECTORIES) message("-- # In child scope, target test property: interface[${dirs_interface}], normal[${dirs_normal}]")target_include_directories/test/test.h文件内容：
#ifndef __TEST_TT__ #define __TEST_TT__ void test_print(); #endiftarget_include_directories/test/test.cpp文件内容：
#include "test.h" #include <iostream> void test_print() { std::cout << "In test: say hello!" << std::endl; }在target_include_directories目录下，运行
cmake .以及make VERBOSE=1，关键输出：$ cmake . …… -- # In child scope, target test property: interface[/home/shengyi/code/gitee_repo/projects/cmake/target_include_directories/test], normal[] # In parent scope, target main property: interface[], normal[] # In parent scope, after add test lib, target main property: interface[], normal[] $ make VERBOSE=1 …… [ 75%] Building CXX object CMakeFiles/main.dir/main.cpp.o /usr/bin/c++ -I/XXX/target_include_directories/test -MD -MT CMakeFiles/main.dir/main.cpp.o -MF CMakeFiles/main.dir/main.cpp.o.d -o CMakeFiles/main.dir/main.cpp.o -c /home/shengyi/code/gitee_repo/projects/cmake/target_include_directories/main.cpp [100%] Linking CXX executable main $ ./main In main... In test: say hello!可见通过PUBLIC或INTERFACE添加到库文件test的目录，也可以传递到可执行文件main（PRIVATE无法传递，可以尝试修改一下）。
2）可执行文件main中直接添加test目录，库文件编译时不添加test目录
与上面的对比，只修改了两个CMakeLists.txt文件，去除了target_include_directories/test/CMakeLists.txt中的target_include_directories语句，在target_include_directories/CMakeLists.txt中通过target_include_directories将test目录增加到目标文件main中。
target_include_directories/CMakeLists.txt文件内容：
cmake_minimum_required(VERSION 3.22) project(target_include_test) add_subdirectory(test) add_executable(main main.cpp) target_include_directories(main PRIVATE test) get_property(dirs_interface TARGET main PROPERTY INTERFACE_INCLUDE_DIRECTORIES) get_property(dirs_normal TARGET main PROPERTY INCLUDE_DIRECTORIES) message("# In parent scope, target main property: interface[${dirs_interface}], normal[${dirs_normal}]") target_link_libraries(main test) get_property(dirs_interface TARGET main PROPERTY INTERFACE_INCLUDE_DIRECTORIES) get_property(dirs_normal TARGET main PROPERTY INCLUDE_DIRECTORIES) message("# In parent scope, after add test lib, target main property: interface[${dirs_interface}], normal[${dirs_normal}]")target_include_directories/CMakeLists.txt文件内容：
add_library(test test.cpp) get_property(dirs_interface TARGET test PROPERTY INTERFACE_INCLUDE_DIRECTORIES) get_property(dirs_normal TARGET test PROPERTY INCLUDE_DIRECTORIES) message("-- # In child scope, target test property: interface[${dirs_interface}], normal[${dirs_normal}]")在target_include_directories目录下，运行
cmake .以及make VERBOSE=1，关键输出：$ cmake . …… -- # In child scope, target test property: interface[], normal[] # In parent scope, target main property: interface[], normal[/XXX/target_include_directories/test] # In parent scope, after add test lib, target main property: interface[], normal[/XXX/target_include_directories/test] $ make VERBOSE=1 …… [ 75%] Building CXX object CMakeFiles/main.dir/main.cpp.o /usr/bin/c++ -I/XXX/target_include_directories/test -MD -MT CMakeFiles/main.dir/main.cpp.o -MF CMakeFiles/main.dir/main.cpp.o.d -o CMakeFiles/main.dir/main.cpp.o -c /home/shengyi/code/gitee_repo/projects/cmake/target_include_directories/main.cpp [100%] Linking CXX executable main $ ./main In main... In test: say hello!
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