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Question

我正在做一个宠物项目并且正在使用 clang++（特别是 MacPorts clang 3.1）。所以我决定切换到 libc++（使用 std::array 等），但我使用的是 boost（特别是 asio 和 regex），所以我不得不使用 libc++ 重新编译 boost。我删除了安装在 macports 中的 boost 并从源代码构建 boost，现在安装在 /usr/local/include 和 /usr/local/lib 中。从那以后，我无法编译。以下是我遇到的奇怪现象：

执行时：

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

我收到一个与移动构造函数有关的奇怪编译错误（此错误还有更多，但正如您所见，它来自 boost）：

/usr/include/c++/v1/string:1952:10: error: overload resolution selected implicitly-deleted copy assignment operator
__r_ = _STD::move(__str.__r_);
     ^
/usr/include/c++/v1/string:1942:9: note: in instantiation of member function 'std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::__move_assign' requested here
    __move_assign(__str, true_type());
    ^
/usr/include/c++/v1/string:1961:5: note: in instantiation of member function 'std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::__move_assign' requested here
__move_assign(__str, integral_constant<bool,
^
/usr/local/include/boost/regex/v4/perl_matcher.hpp:207:16: note: in instantiation of member function 'std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::operator=' requested here
        s1 = traits_inst.transform(a, a + 1);

但是，当我执行时（请注意“-I”，它必须在那个确切的位置）：

clang++ -I -std=c++11 -stdlib=libc++ -g -c main.cpp

这会编译（但稍后链接会失败）。为什么是这样？ -I do without a path 是什么意思？ -stdlib= 必须以 -I 开头吗？

现在是有趣的部分：

尽管现在一切都编译了，但它不会链接。执行时：

clang++ main.o FTPClient.o FTPConnection.o -lboost_system -lboost_regex -std=c++11 -stdlib=libc++  -g  -o cli

我收到消息：

Undefined symbols for architecture x86_64:
"__ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEE6__initIPKcEENS_9enable_ifIXsr21__is_forward_iteratorIT_EE5valueEvE4typeESA_SA_", referenced from:
  boost::re_detail::cpp_regex_traits_implementation<char>::lookup_collatename(char const*, char const*) const in libboost_regex.a(instances.o)
  boost::re_detail::cpp_regex_traits_implementation<char>::lookup_classname_imp(char const*, char const*) const in libboost_regex.a(instances.o)
  boost::re_detail::basic_regex_parser<char, boost::regex_traits<char, boost::cpp_regex_traits<char> > >::fail(boost::regex_constants::error_type, long, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, long) in libboost_regex.a(instances.o)
  boost::re_detail::cpp_regex_traits_implementation<char>::lookup_classname(char const*, char const*) const in libboost_regex.a(instances.o)
  ld: symbol(s) not found for architecture x86_64

现在我想也许我缺少一些 -lboost 标志，但我不确定它是什么。这可能是什么原因？

非常感谢！

编辑：查看安装 boost 的日志时，我注意到了这一点：

..failed clang-darwin.link.dll /usr/local/lib/libboost_filesystem.dylib...
clang-darwin.link.dll /usr/local/lib/libboost_regex.dylib
Undefined symbols for architecture x86_64:
  "__ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEE6__initIPKcEENS_9enable_ifIXsr21__is_forward_iteratorIT_EE5valueEvE4typeESA_SA_", referenced from:
  boost::c_regex_traits<char>::transform(char const*, char const*) in c_regex_traits.o
  boost::c_regex_traits<char>::lookup_classname(char const*, char const*) in c_regex_traits.o
  boost::c_regex_traits<char>::lookup_collatename(char const*, char const*) in c_regex_traits.o
  boost::re_detail::RegExData::update() in cregex.o
  boost::RegEx::What(int) const in cregex.o
  boost::re_detail::pred2::operator()(boost::match_results<char const*, std::__1::allocator<boost::sub_match<char const*> > > const&) in cregex.o
  boost::re_detail::cpp_regex_traits_implementation<char>::lookup_collatename(char const*, char const*) const in instances.o
  ...
  "__ZNSt3__112basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEE6__initIPKwEENS_9enable_ifIXsr21__is_forward_iteratorIT_EE5valueEvE4typeESA_SA_", referenced from:
  boost::c_regex_traits<wchar_t>::transform(wchar_t const*, wchar_t const*) in wc_regex_traits.o


  boost::c_regex_traits<wchar_t>::lookup_classname(wchar_t const*, wchar_t const*) in wc_regex_traits.o
  boost::re_detail::cpp_regex_traits_implementation<wchar_t>::lookup_collatename(wchar_t const*, wchar_t const*) const in winstances.o
  boost::re_detail::cpp_regex_traits_implementation<wchar_t>::lookup_classname_imp(wchar_t const*, wchar_t const*) const in winstances.o
  boost::re_detail::cpp_regex_traits_implementation<wchar_t>::lookup_classname(wchar_t const*, wchar_t const*) const in winstances.o
ld: symbol(s) not found for architecture x86_64  
clang: error: linker command failed with exit code 1 (use -v to see invocation)

这是否意味着 boost 正则表达式可能与 -libc++ 不兼容？

编辑 2：我尝试使用 std::regex，但我明白了：

Undefined symbols for architecture x86_64:
   "__ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEE6__initIPKcEENS_9enable_ifIXsr21__is_forward_iteratorIT_EE5valueEvE4typeESA_SA_", referenced from:
  std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > std::__1::regex_traits<char>::__lookup_collatename<char const*>(char const*, char const*, char) const in main.o
  unsigned int std::__1::regex_traits<char>::__lookup_classname<char const*>(char const*, char const*, bool, char) const in main.o
 ld: symbol(s) not found for architecture x86_64

Answer 1

一个有用但不令人满意的答案：libc++ 包含 std::regex，您可以使用它来代替 boost::regex。