std::multimap compile errors

Question

I am trying to use multimap for the first time but my app will not compile. TIA Paul..

// file dept.h

typedef std::multimap <CString, std::map< CString, CString> > _DeparmentRecord;  // also tryied replacing CString with LPCWSTR

_DeparmentRecord DeparmentRecord;


// file dept.cpp

DWORD CIni::AddNameValue(LPCWSTR Section, LPCWSTR Name, LPCWSTR Value)
{

DeparmentRecord.insert(std::make_pair ( Section, std::make_pair(Name, Value)) );  <-- error here

}

c:\program files\microsoft visual studio 9.0\vc\include\utility(57) : error C2664: 'std::map<_Kty,_Ty>::map(const std::less<_Ty> &)' : cannot convert parameter 1 from 'const std::pair<_Ty1,_Ty2>' to 'const std::less<_Ty> &'

1> with 1> [ 1> _Kty=CString, 1> _Ty=CString 1> ] 1> and 1> [ 1> _Ty1=LPCWSTR, 1> _Ty2=LPCWSTR 1> ] 1> and 1> [ 1> _Ty=CString 1> ] 1> Reason: cannot convert from 'const std::pair<_Ty1,_Ty2>' to 'const std::less<_Ty>' 1> with 1> [ 1> _Ty1=LPCWSTR, 1> _Ty2=LPCWSTR 1> ] 1> and 1> [ 1> _Ty=CString 1> ] 1> No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called 1> c:\dev\projects\migrator\jobbuilder\jobbuilder\ini.cpp(55) : see reference to function template instantiation 'std::pair<_Ty1,_Ty2>::pair>(const std::pair> &)' being compiled 1> with 1> [ 1> _Ty1=const CString, 1> _Ty2=std::map 1> ]

========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

Answer 1

Change the function as follows.

DWORD AddNameValue(LPCWSTR  Section, LPCWSTR  Name, LPCWSTR  Value)
{
    std::map<CString, CString> aTemp;
    aTemp.insert(std::make_pair (Name, Value));
    DeparmentRecord.insert(std::make_pair (Section, aTemp)) ;
}

Answer 2

You're trying to insert a pair< section, pair<...> > into a map that takes pair< section, map<...> >.

Answer 3

std::make_pair(Name, Value) is a pair... but it should be a map.

STL errors can be a true pain. Using the very latest version of GCC can help, its error messages are much improved, but I see you're using MSVC so that's not much help to you.

Answer 4

In addition to the other answers, std::make_pair will return a std::pair. Don't expect the compiler to perform the conversion from LPCWSTR to CString for you.

Answer 5

In addition to the other correct answers, you'll avoid conversion problems (and likely get better error messages) if you use _DeparmentRecord's value_type typedef rather than make_pair.

DWORD AddNameValue(LPCWSTR Section, LPCWSTR Name, LPCWSTR Value)
{
  _DeparmentRecord::iterator i =
      DeparmentRecord.insert(_DeparmentRecord::value_type(Section, v)).first;
  i->second[Name] = Value;
}

And a small point: don't use leading underscores for non-local names - they're reserved for the standard library.