C++ 为什么即使对于私有链接，也会继承包含路径

我有一个简单的项目，包括两个“库”

a

和

b

以及可执行的

c

。我将库

a

（公共）的包含路径设置为

X

（出于测试目的，实际上没有这样的路径）。
现在，

b

与

a

私密链接，

c

与

b

链接。在编译

c.cpp

时，我希望X不在include路径中，因为“它不应该知道

a

，因为它在

b

中是私有的”，但显然它在这里

因此，我的问题是，这是有意的行为还是无意的行为，以及为什么

我的代码：

a、 cpp

b、 cpp

c、 cpp

CMakeLists.txt

cmake_minimum_required(VERSION 2.8)

add_library(a a.cpp)
target_include_directories(a PUBLIC X)

add_library(b b.cpp)
target_link_libraries(b PRIVATE a)

add_executable(c c.cpp)
target_link_libraries(c PUBLIC b)

（详细）编译日志：

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/usr/local/Cellar/cmake/3.8.1/bin/cmake -E cmake_progress_start /Users/alexeyd/test/dir/build/CMakeFiles 6
/Applications/Xcode.app/Contents/Developer/usr/bin/make -f CMakeFiles/Makefile2 CMakeFiles/c.dir/all
/Applications/Xcode.app/Contents/Developer/usr/bin/make -f CMakeFiles/a.dir/build.make CMakeFiles/a.dir/depend
cd /Users/alexeyd/test/dir/build && /usr/local/Cellar/cmake/3.8.1/bin/cmake -E cmake_depends "Unix Makefiles" /Users/alexeyd/test/dir /Users/alexeyd/test/dir /Users/alexeyd/test/dir/build /Users/alexeyd/test/dir/build /Users/alexeyd/test/dir/build/CMakeFiles/a.dir/DependInfo.cmake --color=
Dependee "/Users/alexeyd/test/dir/build/CMakeFiles/a.dir/DependInfo.cmake" is newer than depender "/Users/alexeyd/test/dir/build/CMakeFiles/a.dir/depend.internal".
Dependee "/Users/alexeyd/test/dir/build/CMakeFiles/CMakeDirectoryInformation.cmake" is newer than depender "/Users/alexeyd/test/dir/build/CMakeFiles/a.dir/depend.internal".
Scanning dependencies of target a
/Applications/Xcode.app/Contents/Developer/usr/bin/make -f CMakeFiles/a.dir/build.make CMakeFiles/a.dir/build
[ 16%] Building CXX object CMakeFiles/a.dir/a.cpp.o
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++   -I/Users/alexeyd/test/dir/X   -o CMakeFiles/a.dir/a.cpp.o -c /Users/alexeyd/test/dir/a.cpp
[ 33%] Linking CXX static library liba.a
/usr/local/Cellar/cmake/3.8.1/bin/cmake -P CMakeFiles/a.dir/cmake_clean_target.cmake
/usr/local/Cellar/cmake/3.8.1/bin/cmake -E cmake_link_script CMakeFiles/a.dir/link.txt --verbose=1
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ar qc liba.a  CMakeFiles/a.dir/a.cpp.o
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ranlib liba.a
[ 33%] Built target a
/Applications/Xcode.app/Contents/Developer/usr/bin/make -f CMakeFiles/b.dir/build.make CMakeFiles/b.dir/depend
cd /Users/alexeyd/test/dir/build && /usr/local/Cellar/cmake/3.8.1/bin/cmake -E cmake_depends "Unix Makefiles" /Users/alexeyd/test/dir /Users/alexeyd/test/dir /Users/alexeyd/test/dir/build /Users/alexeyd/test/dir/build /Users/alexeyd/test/dir/build/CMakeFiles/b.dir/DependInfo.cmake --color=
Dependee "/Users/alexeyd/test/dir/build/CMakeFiles/b.dir/DependInfo.cmake" is newer than depender "/Users/alexeyd/test/dir/build/CMakeFiles/b.dir/depend.internal".
Dependee "/Users/alexeyd/test/dir/build/CMakeFiles/CMakeDirectoryInformation.cmake" is newer than depender "/Users/alexeyd/test/dir/build/CMakeFiles/b.dir/depend.internal".
Scanning dependencies of target b
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[ 50%] Building CXX object CMakeFiles/b.dir/b.cpp.o
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++   -I/Users/alexeyd/test/dir/X   -o CMakeFiles/b.dir/b.cpp.o -c /Users/alexeyd/test/dir/b.cpp
[ 66%] Linking CXX static library libb.a
/usr/local/Cellar/cmake/3.8.1/bin/cmake -P CMakeFiles/b.dir/cmake_clean_target.cmake
/usr/local/Cellar/cmake/3.8.1/bin/cmake -E cmake_link_script CMakeFiles/b.dir/link.txt --verbose=1
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ar qc libb.a  CMakeFiles/b.dir/b.cpp.o
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ranlib libb.a
[ 66%] Built target b
/Applications/Xcode.app/Contents/Developer/usr/bin/make -f CMakeFiles/c.dir/build.make CMakeFiles/c.dir/depend
cd /Users/alexeyd/test/dir/build && /usr/local/Cellar/cmake/3.8.1/bin/cmake -E cmake_depends "Unix Makefiles" /Users/alexeyd/test/dir /Users/alexeyd/test/dir /Users/alexeyd/test/dir/build /Users/alexeyd/test/dir/build /Users/alexeyd/test/dir/build/CMakeFiles/c.dir/DependInfo.cmake --color=
Dependee "/Users/alexeyd/test/dir/build/CMakeFiles/c.dir/DependInfo.cmake" is newer than depender "/Users/alexeyd/test/dir/build/CMakeFiles/c.dir/depend.internal".
Dependee "/Users/alexeyd/test/dir/build/CMakeFiles/CMakeDirectoryInformation.cmake" is newer than depender "/Users/alexeyd/test/dir/build/CMakeFiles/c.dir/depend.internal".
Scanning dependencies of target c
/Applications/Xcode.app/Contents/Developer/usr/bin/make -f CMakeFiles/c.dir/build.make CMakeFiles/c.dir/build
[ 83%] Building CXX object CMakeFiles/c.dir/c.cpp.o
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++   -I/Users/alexeyd/test/dir/X   -o CMakeFiles/c.dir/c.cpp.o -c /Users/alexeyd/test/dir/c.cpp
[100%] Linking CXX executable c
/usr/local/Cellar/cmake/3.8.1/bin/cmake -E cmake_link_script CMakeFiles/c.dir/link.txt --verbose=1
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++   -Wl,-search_paths_first -Wl,-headerpad_max_install_names  CMakeFiles/c.dir/c.cpp.o  -o c libb.a liba.a
[100%] Built target c
/usr/local/Cellar/cmake/3.8.1/bin/cmake -E cmake_progress_start /Users/alexeyd/test/dir/build/CMakeFiles 0

日志中有趣的部分：

[ 83%] Building CXX object CMakeFiles/c.dir/c.cpp.o 
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++   -I/Users/alexeyd/test/dir/X   -o CMakeFiles/c.dir/c.cpp.o -c /Users/alexeyd/test/dir/c.cpp

---

我使用CMake 3.8.1

如果指定最低CMake版本>=2.8.12，则不会出现奇怪的行为：

cmake_minimum_required(VERSION 2.8.12)

---

target\u包括目录

和

私有

/

公共

区别在CMake 2.8.12之前不存在。我的看法是，对于比该版本更早的版本，CMake选择在默认情况下将所有内容公开。

旁注：请记住，有两个不同的阶段在起作用；汇编和链接。包含路径仅在编译（查找头文件）期间相关，而在链接期间不相关。链接时，将使用一组不同的路径来搜索要链接的对象文件/库。对于gcc，这就是选项之间的区别。@JesperJuhl我不确定这在这里有什么关系。这主要是一个CMake问题<代码>目标链接库不仅仅与链接器接口；它允许您将CMake目标链接在一起（它还设置了包含目录和其他所有内容）。这里让我吃惊的是，如果

b

私下链接到

c

，则包含路径仍然存在……我甚至可以说，指定

CMake\u所需的最小值（版本3.0）是合理的

现在，我们不希望smth依赖于最低要求的版本，而我使用的版本是相反的

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cd /Users/alexeyd/test/dir/build && /usr/local/Cellar/cmake/3.8.1/bin/cmake -E cmake_depends "Unix Makefiles" /Users/alexeyd/test/dir /Users/alexeyd/test/dir /Users/alexeyd/test/dir/build /Users/alexeyd/test/dir/build /Users/alexeyd/test/dir/build/CMakeFiles/a.dir/DependInfo.cmake --color=
Dependee "/Users/alexeyd/test/dir/build/CMakeFiles/a.dir/DependInfo.cmake" is newer than depender "/Users/alexeyd/test/dir/build/CMakeFiles/a.dir/depend.internal".
Dependee "/Users/alexeyd/test/dir/build/CMakeFiles/CMakeDirectoryInformation.cmake" is newer than depender "/Users/alexeyd/test/dir/build/CMakeFiles/a.dir/depend.internal".
Scanning dependencies of target a
/Applications/Xcode.app/Contents/Developer/usr/bin/make -f CMakeFiles/a.dir/build.make CMakeFiles/a.dir/build
[ 16%] Building CXX object CMakeFiles/a.dir/a.cpp.o
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++   -I/Users/alexeyd/test/dir/X   -o CMakeFiles/a.dir/a.cpp.o -c /Users/alexeyd/test/dir/a.cpp
[ 33%] Linking CXX static library liba.a
/usr/local/Cellar/cmake/3.8.1/bin/cmake -P CMakeFiles/a.dir/cmake_clean_target.cmake
/usr/local/Cellar/cmake/3.8.1/bin/cmake -E cmake_link_script CMakeFiles/a.dir/link.txt --verbose=1
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/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ranlib liba.a
[ 33%] Built target a
/Applications/Xcode.app/Contents/Developer/usr/bin/make -f CMakeFiles/b.dir/build.make CMakeFiles/b.dir/depend
cd /Users/alexeyd/test/dir/build && /usr/local/Cellar/cmake/3.8.1/bin/cmake -E cmake_depends "Unix Makefiles" /Users/alexeyd/test/dir /Users/alexeyd/test/dir /Users/alexeyd/test/dir/build /Users/alexeyd/test/dir/build /Users/alexeyd/test/dir/build/CMakeFiles/b.dir/DependInfo.cmake --color=
Dependee "/Users/alexeyd/test/dir/build/CMakeFiles/b.dir/DependInfo.cmake" is newer than depender "/Users/alexeyd/test/dir/build/CMakeFiles/b.dir/depend.internal".
Dependee "/Users/alexeyd/test/dir/build/CMakeFiles/CMakeDirectoryInformation.cmake" is newer than depender "/Users/alexeyd/test/dir/build/CMakeFiles/b.dir/depend.internal".
Scanning dependencies of target b
/Applications/Xcode.app/Contents/Developer/usr/bin/make -f CMakeFiles/b.dir/build.make CMakeFiles/b.dir/build
[ 50%] Building CXX object CMakeFiles/b.dir/b.cpp.o
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[ 66%] Linking CXX static library libb.a
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/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ar qc libb.a  CMakeFiles/b.dir/b.cpp.o
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ranlib libb.a
[ 66%] Built target b
/Applications/Xcode.app/Contents/Developer/usr/bin/make -f CMakeFiles/c.dir/build.make CMakeFiles/c.dir/depend
cd /Users/alexeyd/test/dir/build && /usr/local/Cellar/cmake/3.8.1/bin/cmake -E cmake_depends "Unix Makefiles" /Users/alexeyd/test/dir /Users/alexeyd/test/dir /Users/alexeyd/test/dir/build /Users/alexeyd/test/dir/build /Users/alexeyd/test/dir/build/CMakeFiles/c.dir/DependInfo.cmake --color=
Dependee "/Users/alexeyd/test/dir/build/CMakeFiles/c.dir/DependInfo.cmake" is newer than depender "/Users/alexeyd/test/dir/build/CMakeFiles/c.dir/depend.internal".
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Scanning dependencies of target c
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[ 83%] Building CXX object CMakeFiles/c.dir/c.cpp.o
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[100%] Linking CXX executable c
/usr/local/Cellar/cmake/3.8.1/bin/cmake -E cmake_link_script CMakeFiles/c.dir/link.txt --verbose=1
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[ 83%] Building CXX object CMakeFiles/c.dir/c.cpp.o 
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cmake_minimum_required(VERSION 2.8.12)