CMake找不到导入的库 [英] CMake can't find IMPORTED library

问题描述

在 foo / CMakeLists.txt 中，基于此和此，我拥有以下

In foo/CMakeLists.txt, based on this and this, I have the following

SET (EXTERNAL_LIB_ROOT "../../external_libs/")

ADD_LIBRARY (avcodec-debug STATIC IMPORTED)

SET_PROPERTY (
    TARGET avcodec-debug PROPERTY IMPORTED_LOCATION
    ${EXTERNAL_LIB_ROOT}/libavcodec-0.8.10.a)

在 bar / CMakeLists.txt 中我有这个：

# old way uses system libraries
#TARGET_LINK_LIBRARIES (bar avformat avcodec avutil)

# new way uses local debug builds
TARGET_LINK_LIBRARIES (bar avformat avcodec-debug avutil)

当我运行 make 我得到

/usr/bin/ld: cannot find -lavcodec-debug

如果我使用旧方法，请进行构建，触摸 foo / CMakeLists.txt 并进行重新构建，CMake的配置输出表明构建系统已找到avcodec-debug 。

If I revert to the old way, build, touch foo/CMakeLists.txt and rebuild, CMake's configuration output indicates that avcodec-debug is being found by the build system.

那为什么我不能将其添加为依赖项？

So why can't I add it as a dependency?

推荐答案

导入的目标与未导入的目标没有遵循相同的可见性规则。虽然非导入目标是全局的（定义后即可在任何地方可见和访问），但是导入目标仅在定义它们的 CMakeLists.txt 中可见（在由 add_subdirectory（）在此定义的CMakeList中添加的目录中。）

Imported targets do not follow the same visibility rules as non-imported targets. While non-imported targets are global (visible and accessible from anywhere after they're defined), imported targets are only visible in the CMakeLists.txt where they are defined and below (in directories added by add_subdirectory() in this defining CMakeList).

由于 foo 是 bar 的兄弟姐妹，目标名称 avcodec-debug 不可见在 bar / CMakeLists.txt 内部，因此将其视为普通库名称。

Since foo is a sibling of bar in your case, the target name avcodec-debug is not visible inside bar/CMakeLists.txt, so it's treated as a normal library name.

通常首选定义导入目标包含在您包含的文件中，而不是它们自己的项目中。因此，将 foo / CMakeLists.txt 更改（或提取其中的相关部分）为 foo / avcodec.cmake ，然后在顶层CMakeList，替换

It's generally preferred to define imported targets in files you include rather than in their own projects. So change (or extract the relevant parts of) foo/CMakeLists.txt into foo/avcodec.cmake and then in the top-level CMakeList, replace

add_subdirectory(foo)

with

include(foo/avcodec.cmake)

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