为什么预先声明 std：：basic_string<T> 会破坏 boost：：regex？

Why does predeclaring std::basic_string<T> break boost::regex?

本文关键字：gt boost regex basic std string lt 为什么 声明      更新时间：2023-10-16

使用Microsoft Visual Studio 2012编译器，以及boost 1.53，我有一些工作代码用于：

#include <boost/regex.hpp>

后来我将以下两行添加到包含在 regex.hpp 之前的头文件中：

namespace std {template<class T> class basic_string<T>;}
typedef std::basic_string<TCHAR> tstring;

现在我得到了一堆编译错误，但如果在其他行之前包含 regex.hpp，则没有错误。

许多错误中的前几个是：

c:program files (x86)boostboost_1_53boostregexv4instances.hpp(106): error C2027: use of undefined type 'std::basic_string<_Elem,_Traits,_Alloc>'
19>          with
19>          [
19>              _Elem=char16_t,
19>              _Traits=std::char_traits<unsigned short>,
19>              _Alloc=std::allocator<char16_t>
19>          ]
19>c:program files (x86)boostboost_1_53boostregexv4instances.hpp(106): error C2065: 'const_iterator' : undeclared identifier
19>c:program files (x86)boostboost_1_53boostregexv4instances.hpp(106): error C2923: 'boost::match_results' : 'const_iterator' is not a valid template type argument for parameter 'BidiIterator'
19>c:program files (x86)microsoft visual studio 11.0vcincludexutility(364): error C2825: '_Iter': must be a class or namespace when followed by '::'
19>          c:program files (x86)boostboost_1_53boostregexv4iterator_traits.hpp(116) : see reference to class template instantiation 'std::iterator_traits<_Iter>' being compiled
19>          with
19>          [
19>              _Iter=int
19>          ]
19>          c:program files (x86)boostboost_1_53boostregexv4match_results.hpp(68) : see reference to class template instantiation 'boost::re_detail::regex_iterator_traits<T>' being compiled
19>          with
19>          [
19>              T=int
19>          ]
19>          c:program files (x86)boostboost_1_53boostregexv4instances.hpp(106) : see reference to class template instantiation 'boost::match_results<BidiIterator>' being compiled
19>          with
19>          [
19>              BidiIterator=int
19>          ]
19>c:program files (x86)microsoft visual studio 11.0vcincludexutility(364): error C2039: 'iterator_category' : is not a member of '`global namespace''
19>c:program files (x86)microsoft visual studio 11.0vcincludexutility(364): error C2146: syntax error : missing ';' before identifier 'iterator_category'
19>c:program files (x86)microsoft visual studio 11.0vcincludexutility(364): error C2602: 'std::iterator_traits<_Iter>::iterator_category' is not a member of a base class of 'std::iterator_traits<_Iter>'
19>          with
19>          [
19>              _Iter=int
19>          ]
19>          c:program files (x86)microsoft visual studio 11.0vcincludexutility(364) : see declaration of 'std::iterator_traits<_Iter>::iterator_category'
19>          with
19>          [
19>              _Iter=int
19>          ]
19>c:program files (x86)microsoft visual studio 11.0vcincludexutility(364): error C2868: 'std::iterator_traits<_Iter>::iterator_category' : illegal syntax for using-declaration; expected qualified-name
19>          with
19>          [
19>              _Iter=int
19>          ]
19>c:program files (x86)microsoft visual studio 11.0vcincludexutility(365): error C2825: '_Iter': must be a class or namespace when followed by '::'
19>c:program files (x86)microsoft visual studio 11.0vcincludexutility(365): error C2039: 'value_type' : is not a member of '`global namespace''
19>c:program files (x86)microsoft visual studio 11.0vcincludexutility(365): error C2146: syntax error : missing ';' before identifier 'value_type'
19>c:program files (x86)microsoft visual studio 11.0vcincludexutility(365): error C2602: 'std::iterator_traits<_Iter>::value_type' is not a member of a base class of 'std::iterator_traits<_Iter>'

请谁能告诉我我的预先声明std：：basic_string有什么问题？

您已经从声明中省略了几个模板参数。正确的看起来像：

template<class charT, class traits = char_traits<charT>,
         class Allocator = allocator<charT> >
class basic_string;

不过，不要尝试自己做这件事。使用<string> .

谁能告诉我我的预先声明有什么问题std::basic_string？

它有三个模板参数：

template<class charT, class traits = char_traits<charT>,
    class Allocator = allocator<charT> >
class basic_string;

但是没有理由自己声明标准类型，正如你已经证明的那样，有一个很好的理由不这样做。所以不要那样做;如果需要声明，请包含标头。

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