CMake中include_directories命令用于在构建(build)中添加包含目录,其格式如下:

include_directories([AFTER|BEFORE] [SYSTEM] dir1 [dir2 ...])

      将给定的目录添加到编译器(compiler)用于搜索包含文件的目录。相对路径被解释为相对于当前源目录。
      包含目录被添加到当前CMakeLists文件的INCLUDE_DIRECTORIES目录属性中。它们也被添加到当前CMakeLists文件中每个目标的INCLUDE_DIRECTORIES目标属性(target property)中。目标属性值是生成器(generator)使用的属性值。
      默认情况下，指定的目录被追加到当前目录列表中。这个默认行为可以通过将CMAKE_INCLUDE_DIRECTORIES_BEFORE设置为ON来改变。通过显式使用AFTER或BEFORE，可以在appending和prepending之间进行选择，而不依赖于默认值。
      如果给出了SYSTEM选项，编译器将被告知在某些平台上目录是系统包含目录。
      include_directories的参数可以使用语法为"$<...>"的"生成器表达式(generator expressions)".
      注意：最好使用target_include_directories命令向单个目标添加包含目录，并可选地将它们传播/导出(propagate/export)到依赖项.

      执行测试代码需要多个文件：

      build.sh内容如下：

#! /bin/bash

# supported input parameters(cmake commands)
params=(function macro cmake_parse_arguments \
		find_library find_path find_file find_program find_package \
		cmake_policy cmake_minimum_required project include \
		string list set foreach message option if while return \
		math file configure_file \
		include_directories)

usage()
{
	echo "Error: $0 needs to have an input parameter"

	echo "supported input parameters:"
	for param in ${params[@]}; do
		echo "  $0 ${param}"
	done

	exit -1
}

if [ $# != 1 ]; then
	usage
fi

flag=0
for param in ${params[@]}; do
	if [ $1 == ${param} ]; then
		flag=1
		break
	fi
done

if [ ${flag} == 0 ]; then
	echo "Error: parameter \"$1\" is not supported"
	usage
	exit -1
fi

if [[ ! -d "build" ]]; then
	mkdir build
	cd build
else
	cd build
fi

echo "==== test $1 ===="

# test_set.cmake: cmake -DTEST_CMAKE_FEATURE=$1 --log-level=verbose ..
# test_option.cmake: cmake -DTEST_CMAKE_FEATURE=$1 -DBUILD_PYTORCH=ON ..
cmake -DTEST_CMAKE_FEATURE=$1 ..
# It can be executed directly on the terminal, no need to execute build.sh, for example: cmake -P test_set.cmake
make

      CMakeLists.txt内容如下：

cmake_minimum_required(VERSION 3.22)
project(cmake_feature_usage)

message("#### current cmake version: ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION}.${CMAKE_PATCH_VERSION}")
include(test_${TEST_CMAKE_FEATURE}.cmake)
message("==== test finish ====")

     test_include_directories.cmake内容如下：

message("#### test_${TEST_CMAKE_FEATURE}.cmake ####")

include_directories(${CMAKE_CURRENT_SOURCE_DIR}/include)
add_executable(sample_add ${CMAKE_CURRENT_SOURCE_DIR}/source/add.cpp ${CMAKE_CURRENT_SOURCE_DIR}/samples/sample_add.cpp)

      另外还包括三个目录：include,source,samples,它们都是非常简单的实现，仅用于测试，如下：

       可能的执行结果如下图所示:

      如果将test_include_directories.cmake中的include_directories命令注释掉，执行则会报找不到头文件的error：

      GitHub： https://github.com/fengbingchun/Linux_Code_Test