Re: linking a C++ lib to an objc tool.

[Jamie Ramone]

On Sun, Aug 27, 2017 at 5:05 AM, David Chisnall <address@hidden> wrote:

Most of the code that I’ve written recently using GNUstep has been Objective-C++, so I can confirm that this work well (though I’m not using gcc, where I believe Objective-C++ still has some rough corners).  Looking at your nm output, it appears as if the symbols are actually there (at least, `_ZN7poppler5imageC2Ev` demangles to `poppler::image::image()`, which is one of the missing symbols.

Your nm output looks like it’s from a .a file though, not a .so.  When resolving symbols in static libraries, GNU linkers only look forwards in the command line, so if you specify `ld a.a b.a` then undefined symbols in `a.a` will be resolved to point to `b.a`, but undefined symbols in `b.a` will not be resolved to point to `a.a`.  You can solve this by either providing the libraries twice (e.g. `ld a.a b.a a.a b.a`), or by using --start-group and --end-group (e.g. `ld --start-group a.a b.a --end-group`), which searches the archives in the group exhaustively until it stops resolving all of the symbols.  Or you can use lld, which doesn’t have this braindead behaviour (which is both user hostile and increases the algorithmic complexity of linking).

No, I specifically typed in "nm ~/Developer/System/lib/libpoppler-cpp.so", so it's not a static lib. Furthermore, I didn't use the -static flag anywhere, and the libs included are done so using -lib_in_question, which is only fore shared libs (static ones are just globed onto the collection of object files during the link stage i.e. gcc a.o b.o c.o static_lib.a, which I don't know how to do in GNUstep make).

 

I’ve found in the past that GNUstep Make’s interfaces for adding linker flags leaves a lot to be desired, because it doesn’t give much control over where things go on the linker command line, but I believe that using the relevant ADDITIONAL_*_LIBS variable will put the -lpoppler-cpp flag at the end of the linker command line, which will make it work.

Is there one for C++ libs? I checked the docs and it mentions GUI, OBJC, and TOOLS. These indicate where, relative to the GNUstep libs in the command line the added libs would go, but I'm not sure where I should put it. I guess it's time to experiment with these...

Thanx!

 

David

On 26 Aug 2017, at 23:03, Jamie Ramone <address@hidden> wrote:
>
> Hello world! I'm trying to build a project of mine in GNUstep which
> requires some functionality provided by an external library, which is
> in C++. I tried to build it with portions in Objc++ but faild. I said
> it couldn't find the symbols it needed (calls to the methods of c++
> objects). So I rewrote the thing moving the c++ dependencies to a
> function in a plain c++ file. Strike 2. I checked around on the web
> and discovered i needed the 'extern "C" {' thingy, so I added that. I
> even rebuilt the external library, knowing that Ubuntu has more bugs
> than rotting wood. Didn't help. I'm all out of ideas. Can anyone help?
> Please let me know what information you need. Thanx!
>

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