Question

I’ve got a large static library in C++ with bits of Objective-C originally built for iOS (armv7).

I built a OS X (64-bit Intel x86_64) version of it, but as soon as I tried to use it in a OS X app project (targeted to Lion 10.7), tens of linker errors appeared, most of them about standard library symbols.

I know how to solve “my” linker problems, but the STD ones copied below are bugging me.

"std::basic_filebuf<char, std::char_traits<char> >::is_open() const"
"std::basic_stringbuf<char, std::char_traits<char>, std::allocator<char> >::str() const"
"std::basic_ios<char, std::char_traits<char> >::widen(char) const"
"std::istream& std::istream::_M_extract<double>(double&)"
"std::ostream::put(char)"
"std::ostream::flush()"
"std::ostream& std::ostream::_M_insert<void const*>(void const*)"
"std::ostream& std::ostream::_M_insert<bool>(bool)"
"std::ostream& std::ostream::_M_insert<double>(double)"
"std::ostream& std::ostream::_M_insert<unsigned long>(unsigned long)"
"std::ostream::operator<<(int)"
"std::ostream::operator<<(short)"
"std::string::_Rep::_M_destroy(std::allocator<char> const&)"
"std::string::_Rep::_S_terminal"
"std::string::_Rep::_S_empty_rep_storage"
"std::string::_Rep::_S_create(unsigned long, unsigned long, std::allocator<char> const&)"
"std::string::append(char const*, unsigned long)"
"std::string::append(std::string const&)"
"std::string::assign(std::string const&)"
"std::string::reserve(unsigned long)"
"std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(char const*, std::allocator<char> const&)"
"std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(std::string const&)"
"std::basic_string<char, std::char_traits<char>, std::allocator<char> >::~basic_string()"
"std::basic_ofstream<char, std::char_traits<char> >::open(char const*, std::_Ios_Openmode)"
"std::basic_ofstream<char, std::char_traits<char> >::close()"
"std::basic_ofstream<char, std::char_traits<char> >::basic_ofstream()"
"std::basic_ofstream<char, std::char_traits<char> >::~basic_ofstream()"
"std::_List_node_base::hook(std::_List_node_base*)"
"std::_List_node_base::unhook()"
"std::basic_stringstream<char, std::char_traits<char>, std::allocator<char> >::basic_stringstream(std::string const&, std::_Ios_Openmode)"
"std::basic_stringstream<char, std::char_traits<char>, std::allocator<char> >::basic_stringstream(std::_Ios_Openmode)"
"std::basic_stringstream<char, std::char_traits<char>, std::allocator<char> >::~basic_stringstream()"
"std::basic_ostringstream<char, std::char_traits<char>, std::allocator<char> >::basic_ostringstream(std::_Ios_Openmode)"
"std::basic_ostringstream<char, std::char_traits<char>, std::allocator<char> >::~basic_ostringstream()"
"std::ios_base::Init::Init()"
"std::ios_base::Init::~Init()"
"std::basic_ios<char, std::char_traits<char> >::clear(std::_Ios_Iostate)"
"std::basic_ostream<char, std::char_traits<char> >& std::__ostream_insert<char, std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*, long)"
"std::_Rb_tree_decrement(std::_Rb_tree_node_base*)"
"std::_Rb_tree_increment(std::_Rb_tree_node_base const*)"
"std::_Rb_tree_increment(std::_Rb_tree_node_base*)"
"std::__throw_logic_error(char const*)"
"std::__throw_length_error(char const*)"
"std::__throw_out_of_range(char const*)"
"std::_Rb_tree_rebalance_for_erase(std::_Rb_tree_node_base*, std::_Rb_tree_node_base&)"
"std::_Rb_tree_insert_and_rebalance(bool, std::_Rb_tree_node_base*, std::_Rb_tree_node_base*, std::_Rb_tree_node_base&)"
"std::cerr"
"std::cout"

I checked my build settings, my project links to the standard library (-stdlib=libc++) and I can use std::cout without any problem in my main.cpp.

I changed the compiler in the build settings from Apple LLVM 4.1 to LLVM GCC 4.2 and the problem disappeared.
I want to keep using Apple LLVM 4.1. How can I fix that?

Thanks!

Answer 1

Change the standard library that is linked to use libstdc++ instead of libc++ – the problem is that the other library was compiled using the g++ mode which uses the libstdc++ library.

Consider the following sample code:

dhcp-191:~/Development/testy/fred% cat fred.cpp
#include <iostream>
#include <string>
#include "fred.h"

using namespace std;

bool dofred(string &x)
{
    cout << x << endl;
    return true;
}
dhcp-191:~/Development/testy/fred% cat fred.h

#include <iostream>
#include <string>

bool dofred(std::string &x);

dhcp-191:~/Development/testy/fred% clang++ -stdlib=libc++ -shared -o fred.dylib fred.cpp
dhcp-191:~/Development/testy/fred% nm fred.dylib | c++filt | grep dofred
0000000000000fa0 T dofred(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >&)
dhcp-191:~/Development/testy/fred% clang++ -stdlib=libstdc++ -shared -o fred.dylib fred.cpp
dhcp-191:~/Development/testy/fred% nm fred.dylib | c++filt | grep dofred                     
0000000000000e30 T dofred(std::string&)

You get two completely different exported symbols. When trying to use the symbol, the app that uses the same -stdlib flag will be able to link, while the app that doesn’t will display a link error.