C++ 为什么可以'；t与libc++；在c++；0x模式链接此boost:：program\u选项示例？

为boost:：program_选项编译此示例代码：

…在MacOS Lion（10.7.2）上，使用与MacPorts一起安装的boost-1.48.0：

$ clang++ -v
Apple clang version 3.0 (tags/Apple/clang-211.12) (based on LLVM 3.0svn)
Target: x86_64-apple-darwin11.2.0
Thread model: posix
$ clang++ -std=c++0x --stdlib=libc++ -lc++ -I/opt/local/include -L/opt/local/lib -lboost_program_options first.cpp -o first
Undefined symbols for architecture x86_64:
  "boost::program_options::options_description::options_description(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, unsigned int, unsigned int)", referenced from:
      _main in cc-6QQcwm.o
  "boost::program_options::operator<<(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, boost::program_options::options_description const&)", referenced from:
      _main in cc-6QQcwm.o
  "boost::program_options::abstract_variables_map::operator[](std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&) const", referenced from:
      boost::program_options::variables_map::operator[](std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&) const in cc-6QQcwm.o
  "boost::program_options::detail::cmdline::set_additional_parser(boost::function1<std::__1::pair<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > >, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&>)", referenced from:
      boost::program_options::basic_command_line_parser<char>::extra_parser(boost::function1<std::__1::pair<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > >, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&>) in cc-6QQcwm.o
  "boost::program_options::detail::cmdline::cmdline(std::__1::vector<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, std::__1::allocator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > > > const&)", referenced from:
      boost::program_options::basic_command_line_parser<char>::basic_command_line_parser(int, char const* const*) in cc-6QQcwm.o
  "boost::program_options::to_internal(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&)", referenced from:
      std::__1::vector<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, std::__1::allocator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > > > boost::program_options::to_internal<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > >(std::__1::vector<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, std::__1::allocator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > > > const&) in cc-6QQcwm.o
  "boost::program_options::invalid_option_value::invalid_option_value(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&)", referenced from:
      void boost::program_options::validate<int, char>(boost::any&, std::__1::vector<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, std::__1::allocator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > > > const&, int*, long) in cc-6QQcwm.o
  "boost::program_options::validation_error::validation_error(boost::program_options::validation_error::kind_t, 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&)", referenced from:
      std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const& boost::program_options::validators::get_single_string<char>(std::__1::vector<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, std::__1::allocator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > > > const&, bool) in cc-6QQcwm.o
  "boost::program_options::value_semantic_codecvt_helper<char>::parse(boost::any&, std::__1::vector<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, std::__1::allocator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > > > const&, bool) const", referenced from:
      vtable for boost::program_options::typed_value<int, char> in cc-6QQcwm.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

$ g++-mp-4.7 -std=c++0x -I/opt/local/include -L/opt/local/lib -lboost_program_options -o first first.cpp

。。。很好。与在没有libc++的情况下使用clang一样：

clang++ -std=c++0x -I/opt/local/include -L/opt/local/lib -lboost_program_options first.cpp -o first

---

怎么了？为什么boost:：program_选项和libc++不能一起工作？

您需要使用clang++-stdlib=libc++重建boost

libc++与gcc的libstdc++不兼容（除了一些低级的东西，比如operatornew）。例如，gcc的libstdc++中的

std:：string

是refcounted，而在libc++中它使用“短字符串优化”。如果您在同一个程序中意外地混合了这两个字符串（并将它们误认为是同一个数据结构），您将不可避免地遇到运行时崩溃

这次事故正是发生在你身上的

---

为了将此运行时崩溃转化为链接时错误，libc++使用名为

inline namespace

的C++11语言功能来更改

std:：string

的ABI，而不影响

std:：string

的API。也就是说，对您来说，

std:：string

看起来是一样的。但是对于链接器，

std:：string

正在被破坏，就好像它在名称空间

std:\uu 1

中一样。因此，链接器知道

std:：basic_string

和

std:：_1:：basic_string

是两种不同的数据结构（前者来自gcc的libstdc+，后者来自libc++）。

看起来链接器找不到合适的64位lib。“ld:未找到架构x86_64的符号”P.s.如何为clang/libc++重新编译boost：一个快速问题。如果我在做我的_stdlib_str.c_str（），那么我最终会被设置为错误，对吗？我的意思是，在这种情况下，上述链接器技巧将被忽略？正确。

内联命名空间

技巧不是防弹的。现在已经足够多年了，我怀疑macOS上的双std:：LIB不再是一个问题。