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

[David Chisnall]

On 27 Aug 2017, at 13:29, Jamie Ramone <address@hidden> wrote:
> 
> 
> 
> 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...

The linker doesn’t know or care what language the libraries are written in.  
The GUI, OBJC, and TOOLS refer to the kind of thing you are building (thing 
that uses AppKit, thing that doesn’t use Foundation or AppKit, thing that uses 
only Foundatiion), not the kind of thing that you are linking it with.

David