Re: Adding external libs to an OOT block

[Ryan Volz]

Hi Dave,

On 2/22/22 11:34 AM, David Cherkus wrote:
> So, I found 
> https://stackoverflow.com/questions/48562304/gnuradio-c-oot-extrernal-so-library 
> <https://stackoverflow.com/questions/48562304/gnuradio-c-oot-extrernal-so-library>
>  which is a very good answer to how to get your OOT block to link to a shared library 
> from another package.
>
>         /As pointed out by the answer of Marcus Müller below I did not link 
> properly. In fact *one has to edit three different cmake files in three places 
> to add an external dynamically loaded library (.so) to an OOT module in 
> GNURadio*. I try to explain briefly what to do:
>         /
>
>          1. /Put a find_package(LIBNAME) in the CMakeLists.txt in the base 
> directory of the OOT module./
>          2. /Corresponding to that a FindLIBNAME.cmake file in the cmake module 
> path is necessary. This file has the purpose to implement the search for 
> include directories and library files (.so files)./
>          3. /Once found the path to the library has to be used with 
> target_link_libraries(...) in lib/CMakeLists.txt (linking)./
>          4. /The include file path, i.e. LIBNAME.h has to be added as include 
> directory using include_directories(...) in the CMakeLists.txt in the base 
> directory of the module.
>             /
>
>         /With ldd it is possible to find out if the external library is linked 
> correctly./
>         /
>         *ldd /usr/local/lib/YOURLIB.so*/
>
> Am wondering if this is documented on the GNUradio web site?  I could use a bit more 
> info, but will give it a go anyway.  I did the C++ tutorial ( 
> https://wiki.gnuradio.org/index.php?title=Guided_Tutorial_GNU_Radio_in_C%2B%2B 
> <https://wiki.gnuradio.org/index.php?title=Guided_Tutorial_GNU_Radio_in_C%2B%2B>
>   ) and this was the very next thing I wanted to do, and I presume many others as 
> well.   I know it's hard to know where to draw the line on teaching enough vs too 
> much, but I think this is a pretty frequent use case, no?  Note that I am teaching 
> myself cmake on the fly.  That's OK, I just taught myself enough C++ to understand 
> the tutorial on the fly as well.
>
> Regards,
> Dave.

This can be easier or harder depending on how well the library you want to link with 
supports CMake. In more detail, you may or may not have to do step 2 of the instructions 
above, and it may be possible to skip 4 as well if the library's include paths are part 
of the target that you "link" with in step 3. So I think it is most helpful to 
ask: what library specifically are you needing to link with?

In general I think covering how to use CMake is best left to the CMake documentation, but 
the GNU Radio tutorials could probably benefit from a simple example of linking with a 
"nice" external library. (That's if they don't already include that somewhere, 
and I can't say that I've looked!)

Cheers,
Ryan