cmake链接libevent的问题

我遇到的问题

根据一般习惯而言，使用cmake链接某个第三方库时，一般先使用find_package()由cmake帮忙找出相应的package。然后，在生成链接时，只需要使用target_link_libraries()即可。

然而上述的方案碰上 链接libevent却失效了。

• 相关背景: 我是通过apt安装的libevent

• 报错信息

  By not providing "FindLibevent.cmake" in CMAKE_MODULE_PATH this project has
  asked CMake to find a package configuration file provided by "Libevent",
  but CMake did not find one.
  
  Could not find a package configuration file provided by "Libevent" with any
  of the following names:
  
      libeventConfig.cmake
      libevent-config.cmake
  
  Add the installation prefix of "Libevent" to CMAKE_PREFIX_PATH or set
  "Libevent_DIR" to a directory containing one of the above files.  If
  "Libevent" provides a separate development package or SDK, be sure it has
  been installed.
  

通过find /usr/share/cmake-3.16/Help/module -name | grep event 确实找不出与libevent相关的文件

解决方法:

使用 event 链接(应该是巧合)

# ...
add_executable(demo <源文件>)

# 注意是event
target_link_libraies(demo event)
#...

根除错误

在cmake的module文件夹下找不到相应库的***Config.cmake文件。
在这里其实大概知道问题所在了。由于我是通过sudo apt-get install libevent-dev 安装的，可能没有帮我将libevent管理模块添加到cmake中，导致find_package找不到。

• 验证

  1. 从github中下载libevent 并传输到linux里
  2. 进入libevent-master/test-export/
  3. 执行下述命令

     & mkdir build && cd build
     & cmake ..
     

  结果出现了一模一样的报错

• 根据文档通过cmake重新安装libevent (重装估计最方便了 \doge \doge)
  libevent/Documentation/Building.md
  最后务必执行 make install

  注意到最后几行字，文件终于回来了: )

  -- Installing: /usr/local/lib/cmake/libevent/LibeventConfig.cmake
  -- Installing: /usr/local/lib/cmake/libevent/LibeventConfigVersion.cmake
  -- Installing: /usr/local/lib/cmake/libevent/LibeventTargets-static.cmake
  -- Installing: /usr/local/lib/cmake/libevent/LibeventTargets-static-release.cmake
  -- Installing: /usr/local/lib/cmake/libevent/LibeventTargets-shared.cmake
  -- Installing: /usr/local/lib/cmake/libevent/LibeventTargets-shared-release.cmake
  

  再操作一下上述的验证步骤,cmake能找到了libevent了

  -- Found libevent include directory: /usr/local/include
  -- Found libevent component: /usr/local/lib/libevent_core.so
  -- Found libevent component: /usr/local/lib/libevent_extra.so
  -- Found libevent component: /usr/local/lib/libevent_openssl.so
  -- Found libevent component: /usr/local/lib/libevent_mbedtls.so
  -- Found libevent component: /usr/local/lib/libevent_pthreads.so
  -- Found libevent 2.2.0 in /usr/local
  

apt 有时很方便，有时可能很麻烦 : (

---

最后附上cmake代码

cmake_minimum_required(VERSION 3.0)

project(demo)

find_package(Libevent REQUIRED)

# LIBEVENT_STATIC_LINK=TRUE
# set(LIBEVENT_STATIC_LIBRARIES "core; extra")

link_directories(
  /usr/local/lib
  /usr/lib
)

include_directories(
  /usr/local/include/
  /usr/include
)

add_compile_options(-Wall)

add_executable(demo demo.cpp)

target_link_libraries(demo libevent::core)