之后如何使导入的目标成为GLOBAL？ [英] How to make imported target GLOBAL afterwards?

问题描述

从CMake 3.8的 FindBoost.cmake 模块中：

From the FindBoost.cmake module of CMake 3.8:

foreach(COMPONENT ${Boost_FIND_COMPONENTS})
  if(_Boost_IMPORTED_TARGETS AND NOT TARGET Boost::${COMPONENT})
    string(TOUPPER ${COMPONENT} UPPERCOMPONENT)
    if(Boost_${UPPERCOMPONENT}_FOUND)
      if(Boost_USE_STATIC_LIBS)
        add_library(Boost::${COMPONENT} STATIC IMPORTED)
      else()
        # Even if Boost_USE_STATIC_LIBS is OFF, we might have static
        # libraries as a result.
        add_library(Boost::${COMPONENT} UNKNOWN IMPORTED)
      endif()

以及该模块的 docu 中的相应注释：

and the corresponding comment from the docu of that module:

重要的是要注意，导入的目标与此模块创建的变量的行为有所不同：同一调用多次find_package（Boost）具有不同选项（例如静态或共享）的目录或子目录将不会覆盖第一次调用创建的目标的值。

It is important to note that the imported targets behave differently than variables created by this module: multiple calls to find_package(Boost) in the same directory or sub-directories with different options (e.g. static or shared) will not override the values of the targets created by the first call.

我认为将目标设为 GLOBAL 是合理的。

I see the rational for having the targets not being GLOBAL.

不过，首选的制作方式是它们是全局的吗？

However, what is the preferred way of making them global?

我习惯于在子目录中定义项目的依赖项，其中包括任何 find_package（...）调用。因此，Boost导入的目标在另一个目录中不可用，例如 /tests/CMakeLists.txt ：

I'm used to defining the dependencies of my project in a sub-directory including any find_package(...) calls. Consequently, the Boost imported targets are not available in another directory, e.g. /tests/CMakeLists.txt:

<project_root>
  /3rdparty
    /git-submodule-of-a-small-lib
    /CMakeLists.txt
  /include
    /...
  /tests
    /CMakeLists.txt
  /CMakeLists.txt

推荐答案

我设法通过包含 3rdparty / CMakeLists.txt 而不是<$ c $来解决全局项目范围中无法使用导入的Boost目标的问题c> add_subdirectory（3rdparty），但是通过 include（3rdparty / CMakeLists.txt）来评估 3rdparty / CMakeLists.txt 在调用者的范围内。

I managed to workaround the problem of having the imported Boost targets not available in the global project scope by including 3rdparty/CMakeLists.txt not by add_subdirectory(3rdparty) but via include(3rdparty/CMakeLists.txt) as this evaluates 3rdparty/CMakeLists.txt in the caller's scope.

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