Question

如何解决以下编译器错误：

xstddef(180): error C2678: binary '<' : no operator found which takes a left-hand operand of type 'const std::string' (or there is no acceptable conversion)
          tuple(572): could be 'bool std::operator <(const std::tuple<> &,const std::tuple<> &)'
          while trying to match the argument list '(const std::string, const std::string)'
          xstddef(179) : while compiling class template member function 'bool std::less<_Ty>::operator ()(const _Ty &,const _Ty &) const'
          with
          [
              _Ty=std::string
          ]
          map(177) : see reference to function template instantiation 'bool std::less<_Ty>::operator ()(const _Ty &,const _Ty &) const' being compiled
          with
          [
              _Ty=std::string
          ]
          type_traits(743) : see reference to class template instantiation 'std::less<_Ty>' being compiled
          with
          [
              _Ty=std::string
          ]
          xtree(1028) : see reference to class template instantiation 'std::is_empty<_Ty>' being compiled
          with
          [
              _Ty=std::less<std::string>
          ]
          map(67) : see reference to class template instantiation 'std::_Tree<_Traits>' being compiled
          with
          [
              _Traits=std::_Tmap_traits<std::string,IDispatcherPtr,std::less<std::string>,std::allocator<std::pair<const std::string,IDispatcherPtr>>,false>
          ]
          main.cpp(506) : see reference to class template instantiation 'std::map<_Kty,_Ty>' being compiled
          with
          [
              _Kty=std::string,
              _Ty=IDispatcherPtr
          ]

代码如下：

class IDispatcher
{
    virtual void operator()() = 0;
};

class AlarmDispatcher: public IDispatcher
{
    virtual void operator()()
    {
    }
};

typedef boost::shared_ptr<IDispatcher> IDispatcherPtr;

int main()
{
    std::map<std::string, IDispatcherPtr> dispatchers;
    dispatchers["alarm"] = boost::make_shared<AlarmDispatcher>();

Answer 1

第一个问题：

您应该明确包含所有必需的标头，而不是通过包含其他标头来间接包含它们：

#include <string> // <== IN PARTICULAR THIS ONE
#include <map>
#include <boost/shared_ptr.hpp>
#include <boost/make_shared.hpp>

根据评论判断，您似乎包含<string.h>标头（标准C库标头）而不是<string>标头which is where the std::string class is defined。

第二个问题：

您忘了在类之间建立继承关系：

class AlarmDispatcher : public IDispatcher
//                    ^^^^^^^^
{
    virtual void operator()()
    {
    }
};

Answer 2

对于那些将来遇到这个问题的人：我通过在函数定义的末尾添加const来解决它，我用它来创建一个可用作c ++ std map集合中的键的类：

bool operator <(const ThisClass& otherInstance)

变为：

bool operator <(const ThisClass& otherInstance) const

二进制'＆lt;' ：找不到map <std :: string，shared_ptr <foo =“”>＆gt; </std :: string，>的运算符

2 个答案: