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

[David Chisnall]

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).

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.

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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