CMapStringToString vs std::map<CString, CString>

Are there any real benefits for me to migrate my useage of CMapStringToString over to std::map<CString, CString> in my application?

I don't understand, I tried to change the code and now it won't compile:

7>------ Build started: Project: Meeting Schedule Assistant, Configuration: Release x64 ------
7>CalendarSettingsOutlookPage.cpp
7>C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.30.30705\include\xhash(112,53): error C2064: term does not evaluate to a function taking 1 arguments
7>C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.30.30705\include\xhash(135): message : see reference to variable template 'const bool _Nothrow_hash<std::hash<ATL::CStringT<wchar_t,StrTraitMFC_DLL<wchar_t,ATL::ChTraitsCRT<wchar_t> > > >,ATL::CStringT<wchar_t,StrTraitMFC_DLL<wchar_t,ATL::ChTraitsCRT<wchar_t> > > >' being compiled
7>C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.30.30705\include\xhash(135): message : while compiling class template member function 'size_t std::_Uhash_compare<_Kty,_Hasher,_Keyeq>::operator ()<_Kty>(const _Keyty &) noexcept(<expr>) const'
7>        with
7>        [
7>            _Kty=CString,
7>            _Hasher=std::hash<CString>,
7>            _Keyeq=std::equal_to<CString>,
7>            _Keyty=ATL::CStringT<wchar_t,StrTraitMFC_DLL<wchar_t,ATL::ChTraitsCRT<wchar_t>>>
7>        ]
7>C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.30.30705\include\xhash(1109): message : see reference to variable template 'const bool _Nothrow_hash<std::_Umap_traits<ATL::CStringT<wchar_t,StrTraitMFC_DLL<wchar_t,ATL::ChTraitsCRT<wchar_t> > >,ATL::CStringT<wchar_t,StrTraitMFC_DLL<wchar_t,ATL::ChTraitsCRT<wchar_t> > >,std::_Uhash_compare<ATL::CStringT<wchar_t,StrTraitMFC_DLL<wchar_t,ATL::ChTraitsCRT<wchar_t> > >,std::hash<ATL::CStringT<wchar_t,StrTraitMFC_DLL<wchar_t,ATL::ChTraitsCRT<wchar_t> > > >,std::equal_to<ATL::CStringT<wchar_t,StrTraitMFC_DLL<wchar_t,ATL::ChTraitsCRT<wchar_t> > > > >,std::allocator<std::pair<ATL::CStringT<wchar_t,StrTraitMFC_DLL<wchar_t,ATL::ChTraitsCRT<wchar_t> > > const ,ATL::CStringT<wchar_t,StrTraitMFC_DLL<wchar_t,ATL::ChTraitsCRT<wchar_t> > > > >,0>,ATL::CStringT<wchar_t,StrTraitMFC_DLL<wchar_t,ATL::ChTraitsCRT<wchar_t> > > >' being compiled
7>C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.30.30705\include\xhash(1096): message : while compiling class template member function 'void std::_Hash<std::_Umap_traits<_Kty,_Ty,std::_Uhash_compare<_Kty,_Hasher,_Keyeq>,_Alloc,false>>::clear(void) noexcept'
7>        with
7>        [
7>            _Kty=CString,
7>            _Ty=CString,
7>            _Hasher=std::hash<CString>,
7>            _Keyeq=std::equal_to<CString>,
7>            _Alloc=std::allocator<std::pair<const CString,CString>>
7>        ]
7>D:\My Programs\2022\MeetSchedAssist\Meeting Schedule Assistant\CalendarSettingsOutlookPage.cpp(156): message : see reference to function template instantiation 'void std::_Hash<std::_Umap_traits<_Kty,_Ty,std::_Uhash_compare<_Kty,_Hasher,_Keyeq>,_Alloc,false>>::clear(void) noexcept' being compiled
7>        with
7>        [
7>            _Kty=CString,
7>            _Ty=CString,
7>            _Hasher=std::hash<CString>,
7>            _Keyeq=std::equal_to<CString>,
7>            _Alloc=std::allocator<std::pair<const CString,CString>>
7>        ]
7>C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.30.30705\include\unordered_map(67): message : see reference to class template instantiation 'std::_Hash<std::_Umap_traits<_Kty,_Ty,std::_Uhash_compare<_Kty,_Hasher,_Keyeq>,_Alloc,false>>' being compiled
7>        with
7>        [
7>            _Kty=CString,
7>            _Ty=CString,
7>            _Hasher=std::hash<CString>,
7>            _Keyeq=std::equal_to<CString>,
7>            _Alloc=std::allocator<std::pair<const CString,CString>>
7>        ]
7>D:\My Programs\2022\MeetSchedAssist\Meeting Schedule Assistant\CalendarSettingsOutlookPage.h(59): message : see reference to class template instantiation 'std::unordered_map<CString,CString,std::hash<CString>,std::equal_to<CString>,std::allocator<std::pair<const CString,CString>>>' being compiled
7>C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.30.30705\include\xhash(111,44): error C2056: illegal expression
7>Done building project "Meeting Schedule Assistant.vcxproj" -- FAILED.

If I use std::map<CString, CString> it works but std::unordered_map<CString, CString> throws out the errors above. My usage calls:

if (m_mapCalendarList.find(strCalendarName) != m_mapCalendarList.end())
if (strCalendarId == m_mapCalendarList[strCalendarName])
m_mapCalendarList.clear();

The variable is defined in the header.

Solution

MFC hash maps have some drawbacks, except from just being not C++ Standard and not portable:

Do not recalculate hash table automatically. Not even able to resize hash table when populated. Default size of hash table may be suboptimal for you.
As noted in comments, they don't support range-based for, or ranges algorithm
Not copyable and not movable by themselves. Moving a container may be useful
Don't support move semantic for element insertion, this involves some overhead

For std::unordered_map, you need to implement hash function, and pass it as the corresponding template parameter. Or specialize standard hash for CString. But I prefer the former option.

And would be good to pass also comparison function, that performs locale-independent comparison. Since with a hash that is not aware of locale, you can't have locale-aware map anyway, but CString::operator== is locale-aware.

As there's HashKey that can take LPCSTR and LPCWSTR that is used by CMap, implementation of own STL-compatible hashes is trivial.

You can completely avoid dealing with hashes, and use std::unordered_map<std::string, std::string>. But transition to std::string will cause way more changes I guess.