CMake Error at CMakeLists.txt:24

比眉伴天荒 2022-02-18 14:47 773阅读 0赞

问题：CMake Error at CMakeLists.txt:24 (add\_subdirectory):  
add\_subdirectory given source "gtest" which is not an existing directory.

解答：

Cmake < 3.11 doesn't support add\_library without any source file, but flann CMake use a trick that use an empty string "" as source list (i.e add\_library(foo SHARED "")).  
The existing flann Cmake code violates the new behavior of add\_library() for Cmake>=3.11.  
[buildroot/buildroot@45a39b3][buildroot_buildroot_45a39b3]

It turns out in Cmake 3.11, "add\_library()" and "add\_executable()" commands can be called without any sources and won't complain as long as sources are added later via "target\_sources()" command.  
[https://blog.kitware.com/cmake-3-11-0-available-for-download/][https_blog.kitware.com_cmake-3-11-0-available-for-download]

Fix is proposed here:  
[mariusmuja/flann\#369][mariusmuja_flann_369]  
The proposed solution is  
(1)create a file named "empty.cpp" under flann/src/cpp/  
(2)change several lines in CMakeLists.txt under flann/src/cpp/CMakeList:  
line 32: add\_library(flann\_cpp SHARED "empty.cpp")  
line 44: add\_library(flann\_cpp SHARED empty.cpp $\{CPP\_SOURCES\})  
line 86: add\_library(flann SHARED "empty.cpp")  
line 90: add\_library(flann SHARED empty.cpp $\{C\_SOURCES\})

[buildroot_buildroot_45a39b3]: https://github.com/buildroot/buildroot/commit/45a39b3e2ba42b72d19bfcef30db1b8da9ead51a
[https_blog.kitware.com_cmake-3-11-0-available-for-download]: https://blog.kitware.com/cmake-3-11-0-available-for-download/
[mariusmuja_flann_369]: https://github.com/mariusmuja/flann/issues/369