cmake find_package, find_library 可以定位到glfw，但是TARGET glfw为false

Question

我的 glfw3 是从源代码构建的，FindGLFW.cmake 用于查找库：

find_path(
  GLFW_INCLUDE_DIR
  NAMES
  GLFW
  PATHS
  include)

find_library(
  GLFW_LIBRARY
  NAMES
  glfw glfw3 glfw3dll
  PATHS
  lib)

include(FindPackageHandleStandardArgs)

find_package_handle_standard_args(GLFW REQUIRED_VARS GLFW_LIBRARY GLFW_INCLUDE_DIR)

我可以在其他项目中使用 find_package(GLFW REQUIRED) 和 target_link_libraries(xxx glfw3)，没有构建错误。但是，if(TARGET glfw) 或 if(TARGET glfw3) 中的语句总是给我错误的结果。可能是什么原因？

示例：

find_package(GLFW REQUIRED)
MESSAGE(STATUS "GLFW: ${GLFW_FOUND}")
if(TARGET glfw)
    MESSAGE(STATUS "Found it")
else()
    MESSAGE(STATUS "Not Found")
endif()
target_link_libraries(xxx glfw3)

这给了我 GLFW: TRUE 和 Not Found 输出，但没有构建错误。

Answer 1

What could be the reason?

您的 cmake 配置中没有名为 glfw 或 glfw3.

的此类目标

请注意，target_link_libraries(xxx glfw3) 很可能正在与库 glfw3 链接，而忽略您的 find_package 调用。我认为你应该做 target_include_directories(xxx ${GLFW_INCLUDE_DIR}) 和 target_link_libraries(xxx ${GLFW_LIBRARY}).

Answer 2

您的 FindGLFW.cmake 文件不足。事实上，根本不需要它或不存在它。 GLFW 已经提供了配置包。以下是构建和使用 any 行为良好的 CMake 包的方法：

首先，获取源代码、构建包并将其安装到本地前缀：

$ git clone https://github.com/glfw/glfw
Cloning into 'glfw'...
remote: Enumerating objects: 27050, done.
remote: Counting objects: 100% (96/96), done.
remote: Compressing objects: 100% (66/66), done.
remote: Total 27050 (delta 40), reused 54 (delta 24), pack-reused 26954
Receiving objects: 100% (27050/27050), 13.27 MiB | 2.87 MiB/s, done.
Resolving deltas: 100% (19047/19047), done.
$ cd glfw/
glfw$ cmake -G Ninja -DCMAKE_BUILD_TYPE=Release -S . -B build
...
-- Generating done
-- Build files have been written to: /path/to/glfw/build
glfw$ cmake --build build
...
glfw$ cmake --install build --prefix install
-- Install configuration: "Release"
-- Installing: /path/to/glfw/install/lib/libglfw3.a
-- Installing: /path/to/glfw/install/include/GLFW
-- Installing: /path/to/glfw/install/include/GLFW/glfw3.h
-- Installing: /path/to/glfw/install/include/GLFW/glfw3native.h
-- Installing: /path/to/glfw/install/lib/cmake/glfw3/glfw3Config.cmake
-- Installing: /path/to/glfw/install/lib/cmake/glfw3/glfw3ConfigVersion.cmake
-- Installing: /path/to/glfw/install/lib/cmake/glfw3/glfw3Targets.cmake
-- Installing: /path/to/glfw/install/lib/cmake/glfw3/glfw3Targets-release.cmake
...

然后为您的示例项目创建一个文件夹，并将您的 CMakeLists.txt 放在那里：

glfw$ mkdir ../glfw-test ; cd ../glfw-test
glfw-test$ vim CMakeLists.txt
glfw-test$ cat CMakeLists.txt
cmake_minimum_required(VERSION 3.20)
project(example)

find_package(glfw3 REQUIRED)

message(STATUS "GLFW: ${glfw3_FOUND}")
if (TARGET glfw)
  message(STATUS "Target exists")
else ()
  message(STATUS "Target does not exist")
endif()

然后您可以构建它并使用 <pkg>_ROOT 变量告诉 CMake 在哪里可以找到 glfw3。如果你在系统范围内安装了这个包，你就不需要设置这个变量。

glfw-test$ cmake -S . -B build -Dglfw3_ROOT=/path/to/glfw/install
...
-- GLFW: 1
-- Target exists
-- Configuring done
-- Generating done
-- Build files have been written to: /path/to/glfw-test/build

cmake find_package, find_library 可以定位到glfw，但是TARGET glfw为false

cmake find_package, find_library can locate glfw, but TARGET glfw is false

c++

cmake

glfw

cmakelists-options