通过＆＃39; const *＆＃39;作为＆＃39;这个＆＃39;如果比较则出错

Question

我收到错误：

  

../ ConcreteRequest.h:23:49：错误：传递'const   std :: map，std :: basic_string＆gt;'as'this'   'std :: map＆lt; _Key，_Tp，_Compare，_ Alloc＆gt; :: mapped_type＆amp;的参数   std :: map＆lt; _Key，_Tp，_Compare，_ Alloc＆gt; :: operator []（std :: map＆lt; _Key，_Tp，   _Compare，_Alloc＆gt; :: key_type＆amp;＆amp;）[with _Key = std :: basic_string; _Tp = std :: basic_string; _Compare = std :: less＆gt ;; _Alloc =   的std ::分配器，   std :: basic_string＆gt;取代; std :: map＆lt; _Key，_Tp，_Compare，   _Alloc＆gt; :: mapped_type = std :: basic_string; std :: map＆lt; _Key，_Tp，_Compare，_Alloc＆gt; :: key_type = std :: basic_string]'丢弃限定符[-fpermissive]

#ifndef CONCRETEREQUEST_H
#define CONCRETEREQUEST_H
#include "RequestFactory.h"
#include "Request.h"
#include "MasterFile.h"
#include <map>
#include <string>
#include <iostream>

class ConcreteRequest : public RequestFactory
{
  Request *createRequest(const std::map<std::string,std::string> &input) const
  {
    std::cout << "==Starting createRequest==" << std::endl;
    Request *pRequest;

    if (input["dataset"] == "masterfile")
      {
        pRequest = new MasterFile(input);
      }

    std::cout << "==Finishing createRequest==" << std::endl;
    return pRequest;
  }
};
#endif

这是if比较。为什么呢？