[CMake] Adding external static library into a target static library

[Robert Maynard]

The example you provided shows how you can combine raw object files
into a single library. As far as I am aware CMake doesn't offer a nice
cross platform API  for extracting the object files from a static
library and adding them to a new static library.



On Thu, Jun 15, 2017 at 10:19 PM, Pawel Veselov <pawel.veselov at gmail.com> wrote:
> Hello.
>
> I looked at this : https://cmake.org/Wiki/CMake/Tutorials/Object_Library,
> and it suggests that I can use target_link_library() to combine static
> libraries together. But I'm utterly failing at it.
>
> Simple:
> add_library(mylib STATIC ${lib_source})
> target_link_libraries(mylib /path/to/libcool.a)
>
> Doesn't work (libcool.a is not appended into mylib.a). If I want to link
> against mylib (inside same cmake), then the libcool.a is added, however,
> into the linkage of the executable that uses mylib.
>
>
> I've tried making it more complicated by separating objects into an object
> library, and then combining that object library and the external .a together
> but it also doesn't do much:
>
> add_library(mylib-obj OBJECT ${lib_source})
> add_library(mylib STATIC $<TARGET_OBJECTS:mylib-obj> /path/to/libcool.a)
>
> or
>
> add_library(mylib-obj OBJECT ${lib_source})
> add_library(mylib STATIC $<TARGET_OBJECTS:mylib-obj>)
> target_link_libraries(mylib /path/to/libcool.a)
>
> In all cases, cmake schedules ar on the object files, and ranlib on the
> result.
>
> Also, it seems it's not possible to create an empty library and add
> other libraries as dependencies, which, in case of static libraries,
> would make sense...
>
> So, is is possible to, using cmake (and not do manual ar manipulations),
> to create a static library containing objects from another static library,
> external to the project?
>
> Thank you!
>
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