使用lambda的多图谓词

本文介绍了使用lambda的多图谓词的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 29岁程序员，3月因学历无情被辞！ std：我尝试使用多图表对一些关系数据进行排序， ：multimap std :: vector< Message>，std :: string， bool（*）（const std :: vector< Message>，const std :: vector< Message> sortmap（[&]（const std :: vector< Message>& lhs， const std :: vector< Message>& rhs）{ return lhs.size < rhs.size（）; }）; 这些类型似乎是正确的，但视觉工作室另有说明。解决方案我将介绍一些提到的选项： 选项1 @Joachim Pilborg auto comparator = []（const std :: vector< Message>& lhs， const std :: vector< Message>& rhs）{ return lhs.size（） rhs.size（）; }; std :: multimap< std :: vector< Message>，std :: string，decltype（comparator）> sortmap（比较器）; 消息msg; std :: vector< Message>消息; messages.push_back（msg）; std :: string str; auto test = std :: make_pair（messages，str）; sortmap.emplace（test）; 会导致 code> 1> c：\program files（x86）\microsoft visual studio 12.0 \vc\include\xtree（1007）：错误C3497：您不能构造lambda的实例 1。 c：\program files（x86）\microsoft visual studio 12.0 \vc\include\xtree（1006）：在编译类模板成员函数'main ::< lambda_2efe1f793bd1dfe8b84381ab9a3a87dc> std :: _ Tree_comp< false，_Traits> :: _ Getcomp（void）const' 1> with 1> [ 1> _Traits = std :: _Tmap_traits< std :: vector< Message，std :: allocator< Message>>，std :: string，main ::< lambda_2efe1f793bd1dfe8b84381ab9a3a87dc> ;, std :: allocator< std :: pair& ：vector< Message，std :: allocator< Message>>，std :: string>>，true> 1> ] 1> c：\program files（x86）\microsoft visual studio 12.0 \vc\include\xtree（1789）：参见函数模板实例化'main ::< lambda_2efe1f793bd1dfe8b84381ab9a3a87dc> std :: _ Tree_comp 1> with 1> [ 1> _Traits = std :: _Tmap_traits< std :: vector< Message，std :: allocator< Message>>，std :: string，main ::< lambda_2efe1f793bd1dfe8b84381ab9a3a87dc> ;, std :: allocator< std :: pair& ：vector< Message，std :: allocator< Message>>，std :: string>>，true> 1> ] 1> c：\program files（x86）\microsoft visual studio 12.0 \vc\include\xtree（1024）：参考类模板实例化'std :: _ Tree_comp< false，_Traits& b 1> with 1> [ 1> _Traits = std :: _Tmap_traits< std :: vector< Message，std :: allocator< Message>>，std :: string，main ::< lambda_2efe1f793bd1dfe8b84381ab9a3a87dc> ;, std :: allocator< std :: pair& ：vector< Message，std :: allocator< Message>>，std :: string>>，true> 1> ] 1> c：\program files（x86）\microsoft visual studio 12.0 \vc\include\map（275）：参见类模板实例化的参考std :: _ Tree< std :: _ Tmap_traits< _Kty，_Ty，_Pr ，_Alloc，true>>'正在编译 1> with 1> [ 1> _Kty = std :: vector< Message，std :: allocator< Message>> 1> ，_Ty = std :: string 1> ，_Pr = main ::< lambda_2efe1f793bd1dfe8b84381ab9a3a87dc> 1> ，_Alloc = std :: allocator< std :: pair< const std :: vector< Message，std :: allocator< Message>>，std :: string> 1> ] 1> c：\users\c\documents\visual studio 2013\projects\project1\project1\source.cpp（15）：参见类模板实例化'std :: multimap< std :: vector< ; Message，std :: allocator< _Ty>>，std :: string，main ::< lambda_2efe1f793bd1dfe8b84381ab9a3a87dc>，std :: allocator< std :: pair< const _Kty，std :: basic_string< char，std :: char_traits< ; char>，std :: allocator< char>>>>>'正在编译 1> with 1> [ 1> _Ty = Message 1> ，_Kty = std :: vector< Message，std :: allocator< Message>> 1> ] 选项2 @PlasmaHH std :: multimap< std :: vector< Message>，std :: string， bool（*）（const std :: vector< Message>& const std :: vector< Message>& sortmap（[&]（const std :: vector< Message>& lhs， const std :: vector< Message>& rhs）{ return lhs.size < rhs.size（）; }）; 消息msg; std :: vector< Message>消息; messages.push_back（msg）; std :: string str; auto test = std :: make_pair（messages，str）; sortmap.emplace（test）; 这个DOES编译，但奇怪的是在可视工作室错误列表中留下错误（并留下恼人的红色波浪）： 1 IntelliSense：没有构造函数的实例std :: multimap< _Kty，_Ty，_Pr，_Alloc> :: multimap [with _Kty = std :: vector< Message，std :: allocator< Message>>>，_Ty = std :: string，_Pr = bool（*）（const std :: vector< Message，std :: allocator< Message> >&& const std :: vector< Message，std :: allocator< Message>&），_Alloc = std :: allocator< std :: pair< const std :: vector< Message，std :: allocator< ; message>>，std :: string>>]匹配参数列表参数类型是：（lambda [] bool（const std :: vector< Message，std :: allocator< Message> & lhs，const std :: vector< Message，std :: allocator< Message>& rhs） - > bool）c：\Users\c\Documents\Visual Studio 2013\Projects\\ \\ Project1\Project1\Source.cpp 12 } 我宁愿用 auto comparator = []（const std :: vector< Message> & lhs， const std :: vector< Message> & rhs）{ return lhs.size（）< rhs.size（）; }; std :: multimap< std :: vector< Message>，std :: string， std :: function< bool（const std :: vector< Message>& const std :: vector< Message>&）>> sortmap（comparator）; 消息msg; std :: vector< Message>消息; messages.push_back（msg）; std :: string str; auto test = std :: make_pair（messages，str）; sortmap.emplace（test）; 选项1似乎无效： https://connect.microsoft.com/VisualStudio/feedback/details/727957/vc11-beta-compiler-fails-to-compile-lambda-key-compalle-for-maps-and-sets 显式定义类型工作，并且由于某种原因使用std :: function使得（烦人的）红色波动和错误列表条目消失。希望这有助于！ I am trying to sort some relational data using a multimap but am having issues getting the predicate defined correctly. std::multimap< std::vector<Message>, std::string, bool (*)(const std::vector<Message>, const std::vector<Message>)> sortmap([&](const std::vector<Message> &lhs, const std::vector<Message> &rhs) { return lhs.size() < rhs.size(); });The types seem to be correct but visual studio says otherwise. 解决方案 I'll go through some of the options mentioned:Option 1 @Joachim Pilborg auto comparator = [](const std::vector<Message>& lhs, const std::vector<Message>& rhs) { return lhs.size() < rhs.size(); }; std::multimap<std::vector<Message>, std::string, decltype(comparator)> sortmap(comparator); Message msg; std::vector<Message> messages; messages.push_back(msg); std::string str; auto test = std::make_pair(messages, str); sortmap.emplace(test);results in 1>c:\program files (x86)\microsoft visual studio 12.0\vc\include\xtree(1007): error C3497: you cannot construct an instance of a lambda1> c:\program files (x86)\microsoft visual studio 12.0\vc\include\xtree(1006) : while compiling class template member function 'main::<lambda_2efe1f793bd1dfe8b84381ab9a3a87dc> std::_Tree_comp<false,_Traits>::_Getcomp(void) const'1> with1> [1> _Traits=std::_Tmap_traits<std::vector<Message,std::allocator<Message>>,std::string,main::<lambda_2efe1f793bd1dfe8b84381ab9a3a87dc>,std::allocator<std::pair<const std::vector<Message,std::allocator<Message>>,std::string>>,true>1> ]1> c:\program files (x86)\microsoft visual studio 12.0\vc\include\xtree(1789) : see reference to function template instantiation 'main::<lambda_2efe1f793bd1dfe8b84381ab9a3a87dc> std::_Tree_comp<false,_Traits>::_Getcomp(void) const' being compiled1> with1> [1> _Traits=std::_Tmap_traits<std::vector<Message,std::allocator<Message>>,std::string,main::<lambda_2efe1f793bd1dfe8b84381ab9a3a87dc>,std::allocator<std::pair<const std::vector<Message,std::allocator<Message>>,std::string>>,true>1> ]1> c:\program files (x86)\microsoft visual studio 12.0\vc\include\xtree(1024) : see reference to class template instantiation 'std::_Tree_comp<false,_Traits>' being compiled1> with1> [1> _Traits=std::_Tmap_traits<std::vector<Message,std::allocator<Message>>,std::string,main::<lambda_2efe1f793bd1dfe8b84381ab9a3a87dc>,std::allocator<std::pair<const std::vector<Message,std::allocator<Message>>,std::string>>,true>1> ]1> c:\program files (x86)\microsoft visual studio 12.0\vc\include\map(275) : see reference to class template instantiation 'std::_Tree<std::_Tmap_traits<_Kty,_Ty,_Pr,_Alloc,true>>' being compiled1> with1> [1> _Kty=std::vector<Message,std::allocator<Message>>1> , _Ty=std::string1> , _Pr=main::<lambda_2efe1f793bd1dfe8b84381ab9a3a87dc>1> , _Alloc=std::allocator<std::pair<const std::vector<Message,std::allocator<Message>>,std::string>>1> ]1> c:\users\c\documents\visual studio 2013\projects\project1\project1\source.cpp(15) : see reference to class template instantiation 'std::multimap<std::vector<Message,std::allocator<_Ty>>,std::string,main::<lambda_2efe1f793bd1dfe8b84381ab9a3a87dc>,std::allocator<std::pair<const _Kty,std::basic_string<char,std::char_traits<char>,std::allocator<char>>>>>' being compiled1> with1> [1> _Ty=Message1> , _Kty=std::vector<Message,std::allocator<Message>>1> ]Option 2 @PlasmaHH std::multimap< std::vector<Message>, std::string, bool (*)(const std::vector<Message> &, const std::vector<Message> &)> sortmap([&](const std::vector<Message> &lhs, const std::vector<Message> &rhs) { return lhs.size() < rhs.size(); }); Message msg; std::vector<Message> messages; messages.push_back(msg); std::string str; auto test = std::make_pair(messages, str); sortmap.emplace(test);This DOES compile, but strangely leaves an error in visual studios error list (and leaves an annoying red squiggle): 1 IntelliSense: no instance of constructor "std::multimap<_Kty, _Ty, _Pr, _Alloc>::multimap [with _Kty=std::vector<Message, std::allocator<Message>>, _Ty=std::string, _Pr=bool (*)(const std::vector<Message, std::allocator<Message>> &, const std::vector<Message, std::allocator<Message>> &), _Alloc=std::allocator<std::pair<const std::vector<Message, std::allocator<Message>>, std::string>>]" matches the argument list argument types are: (lambda []bool (const std::vector<Message, std::allocator<Message>> &lhs, const std::vector<Message, std::allocator<Message>> &rhs)->bool) c:\Users\c\Documents\Visual Studio 2013\Projects\Project1\Project1\Source.cpp 12}I instead settle with auto comparator = [](const std::vector<Message> &lhs, const std::vector<Message> &rhs) { return lhs.size() < rhs.size(); }; std::multimap<std::vector<Message>, std::string, std::function<bool(const std::vector<Message> &, const std::vector<Message> &) >> sortmap(comparator); Message msg; std::vector<Message> messages; messages.push_back(msg); std::string str; auto test = std::make_pair(messages, str); sortmap.emplace(test);Option 1 appears not to work:https://connect.microsoft.com/VisualStudio/feedback/details/727957/vc11-beta-compiler-fails-to-compile-lambda-key-comparer-for-maps-and-setsexplicitly defining the type works, and using std::function for some reason makes the (annoying!!) red squiggle and error list entry go away. Hope this helps! 这篇关于使用lambda的多图谓词的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！ 上岸，阿里云！