use reference in std::map

Question

I want to use reference in std::map

typedef const std::function<void(const cocos2d::Ref*)>& callBack;

std::map<const std::string&, callBack> m_mapListener

and my error message is:

error C2535: 'const std::function<void (const cocos2d::Ref *)> &std::map<const std::string &,callBack,
std::less<_Kty>,std::allocator<std::pair<_Kty,_Ty>>>::operator [](const std::basic_string
<char,std::char_traits<char>,std::allocator<char>> &)' : 
member function already defined or declared 
C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\include\map

How could I fix it?

This has nothing to do with the std::function. Next time perform some experimentation, such as taking away the std::function and seeing whether your problem remains (which it does). Also, present proper testcases in your questions: here your error message complains about operator[], but you don't ever show us actually using operator[]. It's pure chance that we can fix the problem for you regardless. — Lightness Races in Orbit
– Lightness Races in Orbit, Commented Jan 22, 2016 at 10:16

Dimitrios Bouzas · Accepted Answer · 2016-01-22 10:14:34Z

3

Define your map as:

std::map<std::string, callBack> m_mapListener;

STL containers don't support references because they require that their element type meets the requirements of Erasable, in which case references don't.

answered Jan 22, 2016 at 10:14

Dimitrios Bouzas

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