Linking C++ library (libtorrent) from Objective-C - c++

Question

I'm trying to use libtorrent library from Xcode 5.0 Objective-C Project without success.
I've built boost 1.54 and libtorrent-rasterbar (latest) from sources using LLVM 5.0, no problems with that. Also, via MacPorts I obtained pkg-config to get the proper cflags for libtorrent-rasterbar library. From my build settings, the output for pkgconfig libs and cflags were:
-DTORRENT_USE_OPENSSL -DWITH_SHIPPED_GEOIP_H
-DBOOST_ASIO_HASH_MAP_BUCKETS=1021
-DBOOST_EXCEPTION_DISABLE -DBOOST_ASIO_ENABLE_CANCELIO
-DBOOST_ASIO_DYN_LINK -DTORRENT_LINKING_SHARED -I/usr/local/include
-I/usr/local/include/libtorrent
-L/usr/local/lib -ltorrent-rasterbar
Naturally, I added those parameters to Xcode "Linker Flags" and "C/C++ Flags" settings.
Unfortunately, I cannot get my called functions to link right. This is a sample class I wrote in a testclass.cpp file:
#include "libtorrent/entry.hpp"
#include "libtorrent/bencode.hpp"
#include "libtorrent/torrent_info.hpp"
#include "libtorrent/file.hpp"
#include "libtorrent/storage.hpp"
#include "libtorrent/hasher.hpp"
#include "libtorrent/create_torrent.hpp"
void testclass::addFilesFromPath(const char* path)
{
libtorrent::file_storage fs;
libtorrent::add_files(fs, path);
}
Tried to get called from a createpackage.mm file:
testclass* pPackage = new testclass();
testclass->addFilesFromPath([_sessionDir UTF8String]);
The linker cannot found the symbols, output is:
Undefined symbols for architecture x86_64:
"libtorrent::parent_path(std::__1::basic_string, std::__1::allocator > const&)",
referenced from:
libtorrent::add_files(libtorrent::file_storage&, std::__1::basic_string,
std::__1::allocator > const&, unsigned int) in
createpackage.o
"libtorrent::detail::add_files_impl(libtorrent::file_storage&,
std::__1::basic_string,
std::__1::allocator > const&, std::__1::basic_string, std::__1::allocator > const&,
boost::function, std::__1::allocator >)>, unsigned
int)", referenced from:
libtorrent::add_files(libtorrent::file_storage&, std::__1::basic_string,
std::__1::allocator > const&, unsigned int) in
createpackage.o
"libtorrent::complete(std::__1::basic_string, std::__1::allocator > const&)",
referenced from:
libtorrent::add_files(libtorrent::file_storage&, std::__1::basic_string,
std::__1::allocator > const&, unsigned int) in
createpackage.o
"libtorrent::filename(std::__1::basic_string, std::__1::allocator > const&)",
referenced from:
libtorrent::add_files(libtorrent::file_storage&, std::__1::basic_string,
std::__1::allocator > const&, unsigned int) in
createpackage.o ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see
invocation)
I'm pretty puzzled. Checked that libtorrent-raster bar architecture is x86_64. Also, boost is built OK. I'm new to this C++ / Objetive-C code mixing approach.
Thanks.
EDIT 1:
I've resorted to a minimal sample. Made the following CPP file:
#include "libtorrent/file.hpp"
#include "libtorrent/storage.hpp"
#include "libtorrent/create_torrent.hpp"
int main()
{
libtorrent::file_storage fs;
libtorrent::add_files(fs, ".");
}
At command line, tried:
c++ test.cpp $(pkg-config /usr/local/lib/pkgconfig/libtorrent-rasterbar.pc --cflags --libs) -lboost_system
Build is successful. So I wonder how to put all that pkg-config data into the proper target configurations in OSX.

Answer 1

Finally, problem was solved.
Let's check symbols comparing the produced object file and the symbols contained in libtorrent library.
nm createpackage.o|grep 'add_files'
U __ZN10libtorrent6detail14add_files_implERNS_12file_storageERKNSt3__112basic_stringIcNS3_11char_traitsIcEENS3_9allocatorIcEEEESB_N5boost8functionIFbS9_EEEj
00000000000002a0 S __ZN10libtorrent9add_filesERNS_12file_storageERKNSt3__112basic_stringIcNS2_11char_traitsIcEENS2_9allocatorIcEEEEj
00000000000018e0 S __ZN10libtorrent9add_filesERNS_12file_storageERKNSt3__112basic_stringIcNS2_11char_traitsIcEENS2_9allocatorIcEEEEj.eh
Compare with:
$ nm libtorrent-rasterbar.a | grep 'add_files'
00000000000002f0 T __ZN10libtorrent6detail14add_files_implERNS_12file_storageERKSsS4_N5boost8functionIFbSsEEEj
0000000000006e68 S __ZN10libtorrent6detail14add_files_implERNS_12file_storageERKSsS4_N5boost8functionIFbSsEEEj.eh
The difference as many could imagine seeing that output, it's that i'm using the LLVM Standard C++ library for my .mm files while libtorrent was compiled with GCC Stdlib, that's the reason of different symbols referring to char_traits, basic_string, etc.
So, changing in XCode Build Settings > Standard C++ Library to libstdc++ fixed the problem.