Question

Attempting to get a very simple example of libconfig++ working. However I’m encountering the following link error due to the compiler options ‘-stdlib=libc++’ and ‘-std=c++11’.

Environment

Darwin iMac.local 12.2.0

Darwin Kernel Version 12.2.0

xnu-2050.18.24~1/RELEASE_X86_64 x86_64

Source

  Config cfg;

  cfg.readFile( "example.cfg" );

  string value = "";

  const string& key = "application.base";

  cfg.lookupValue( key, value );

Build

clang++ -o main main.cpp -lconfig++ -stdlib=libc++ -std=c++11

Error

Undefined symbols for architecture x86_64:   "libconfig::Config::lookupValue(char   const*, std::__1::basic_string<char, std::__1::char_traits<char>,   std::__1::allocator<char> >&) const", referenced from:  
      libconfig::Config::lookupValue(std::__1::basic_string<char,   std::__1::char_traits<char>, std::__1::allocator<char> > const&,   std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >&)   const in main-mFa01w.o ld: symbol(s) not found for architecture x86_64 clang:   error:   linker command failed with exit code 1 (use -v to see invocation)  

Answer 1

The error message indicates that this member function:

libconfig::Config::lookupValue(const std::string& path, std::string& value) const;

was compiled with -stdlib=libc++ (likely as an inline, but I’m guessing). And that it in turn calls this member function:

libconfig::Config::lookupValue(char const* path, std::string& value) const

However this latter function was not compiled with -stdlib=libc++.

The most probable fix is to recompile libconfig++ with -stdlib=libc++.