Question

The thing is, I am not (knowing trying to use any default constructor of beatle::beatle
the error:

1>  ecosystem.cpp
1>c:\program files (x86)\microsoft visual studio 10.0\vc\include\map(172): error C2512: 'beatle::beatle' : no appropriate default constructor available
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\map(165) : while compiling class template member function 'beatle &std::map<_Kty,_Ty>::operator [](int &&)'
1>          with
1>          [
1>              _Kty=tokenID,
1>              _Ty=beatle
1>          ]
1>          c:\users\zak\documents\visual studio 2010\projects\ascii_sivvure\ascii_sivvure\ecosystem.h(22) : see reference to class template instantiation 'std::map<_Kty,_Ty>' being compiled
1>          with
1>          [
1>              _Kty=tokenID,
1>              _Ty=beatle
1>          ]

Code with non relevant things stripped:

header:

typedef std::map<tokenID,beatle>    Beatles;

class ecosystem
{
private:
line 22:    Beatles m_Beatles;
};

source:

ecosystem::ecosystem(): m_output( output() )
{
    Beatles m_Beatles;
}

void ecosystem::populate()
{
    if (m_isMatingSeason && ( random(0,1000) < rateMATING ) )
    {
        beatle babyBeatle = breed();
        m_Beatles[babyBeatle.getTokenID()] = babyBeatle;
        m_field.occupy(babyBeatle.getTokenID(), babyBeatle.getLocation() );
    }
}

I’ve been trying for hours using different combinations of trying to properly define/declare the maps. At one point intellisense starting saying it wanted pointers to object here:

m_Beatles[babyBeatle.getTokenID()] = babyBeatle;

and that led me down a sad path.

This is all happening after my first(and hopefully last) refactoring binge, its been over a week since I’ve been able to compile… I probably have 40 hours just trying to get it working again.

Answer 1

std::map<>::operator[] requires a default constructor. This is because it first creates an entry in the map then does the operator= that you are calling.

If you absolutely want to use an std::map but do not want to provide a default constructor (perhaps it is illogical for your case?) you can use:

std::map<>::insert()

To explicitly insert the object into the code. This makes things a bit more complicated then because look ups must also use find.

I just noticed that Adam Rosenfield already posted this info in a comment but going ahead and leaving this as a separate answer.