[CMake] Single library with both shared and static binaries

[Juan Sanchez]

Here is an example where two libraries are created from object files that
have only been compiled once:

ADD_LIBRARY(symdiff_objects OBJECT ${CXX_SRCS} ${MC_SRCS})
set_property(TARGET symdiff_objects PROPERTY POSITION_INDEPENDENT_CODE ON)
ADD_LIBRARY(symdiff_dynamic STATIC $<TARGET_OBJECTS:symdiff_objects>)
ADD_LIBRARY(symdiff SHARED $<TARGET_OBJECTS:symdiff_objects>)

The "symdiff_dynamic" library is a static archive that can then be linked
into another shared library or an executable. The "symdiff" library is a
standalone object.  The POSITION_INDEPENDENT_CODE property is required for
the linux platform, but not for macOS or Windows.  If the original poster
is comfortable with having a PIC static library, this is an approach they
can take.

Regards,

Juan

On Wed, Sep 25, 2019 at 8:43 AM Kyle Edwards via CMake <cmake at cmake.org>
wrote:

> On Tue, 2019-09-24 at 23:41 +0300, Avraham Shukron wrote:
> > Hi!
> >
> > I have a library which I want to distribute in both shared object and
> > static library forms.
> > Is there a modern way to do it without creating two completely
> > separate library targets?
> > Since I want to be a good CMake citizen I use `target_*` and
> > `set_target_properties` as much as possible, and creating two
> > different libraries will force me to duplicate that information about
> > each one of them.
> >
> > I also tries not specifying STATIC/SHARED, and then running cmake
> > twice - once with BUILD_SHARED_LIBS=ON and once OFF and then
> > installing to the same directory. I got my both .a and .so libraries
> > installed, but I couldn't get the Config file correctly for this
> > arrangement.
> >
> > So - what is the community-recommended pattern to do this?
>
> Unfortunately, the recommendation is to do exactly what you don't want
> to do: create a shared target and a static target.
>
> To make this slightly simpler, you can use functions to de-duplicate
> the target_* and set_target_properties calls:
>
> function(create_foo_target name type)
>   add_library(${name} ${type} foo.c foo.h)
>   set_target_properties(${name} OUTPUT_NAME foo)
> endfunction()
>
> create_foo_target(foo_shared SHARED)
> create_foo_target(foo_static STATIC)
>
> Kyle
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