vector holding read-only matrices?

Question

I want to use a vector to hold read-only integer-matrices of the size 5x5

vector<const int[5][5]> startingPieces;

But this declaration causes a bunch of weird errors I've never ever seen before.

error C2535: 'const int (*std::allocator<_Ty>::address(const int (&)[5][5]) const)[5][5]' : member function already defined or declared
1>        with
1>        [
1>            _Ty=const int [5][5]
1>        ]
1>        c:\program files\microsoft visual studio 9.0\vc\include\xmemory(109) : see declaration of 'std::allocator<_Ty>::address'
1>        with
1>        [
1>            _Ty=const int [5][5]
1>        ]
1>        c:\program files\microsoft visual studio 9.0\vc\include\vector(429) : see reference to class template instantiation 'std::allocator<_Ty>' being compiled
1>        with
1>        [
1>            _Ty=const int [5][5]
1>        ]
1>        c:\program files\microsoft visual studio 9.0\vc\include\vector(439) : see reference to class template instantiation 'std::_Vector_val<_Ty,_Alloc>' being compiled
1>        with
1>        [
1>            _Ty=const int [5][5],
1>            _Alloc=std::allocator<const int [5][5]>
1>        ]
1>        c:\users\eric\documents\visual studio 2008\projects\testing grounds\testing grounds\main.cpp(14) : see reference to class template instantiation 'std::vector<_Ty>' being compiled
1>        with
1>        [
1>            _Ty=const int [5][5]
1>        ]

So, what is wrong with this declaration?

score 7 · Answer 1 · edited May 23 '17 at 12:06

7

Two things - firstly vectors cannot hold const objects - see Can I use const in vectors to allow adding elements, but not modifications to the already added? for a discussion of this. And secondly they cannot hold arrays, as the things they hold must be copyable and assignable, and arrays are neither.

edited May 23 '17 at 12:06

Community

1
1

answered Jun 17 '10 at 14:03

score 2 · Accepted Answer · answered Jun 17 '10 at 14:05

2

What you should do here is create your own matrix class that stores the 5x5 array of data and then create your vector with that.

answered Jun 17 '10 at 14:05

bshields

3,563
16
16

Yes,that does seem like easiest solution to this problem. – Eric Jun 17 '10 at 14:11

score 1 · Answer 3 · answered Jun 17 '10 at 14:06

1

One option is to use the array class (your implementation may support std::array or std::tr1::array; if not, you can use boost::array from the Boost libraries):

std::vector<std::array<std::array<int, 5> > >

The elements stored in the container still cannot be const; you can make the entire vector const if that works for your use case.

answered Jun 17 '10 at 14:06

James McNellis

348,265
75
913
977

I'll throw in here that `blitz::Array` also works pretty well for me, though it doesn't really do read-only. – kenm Jun 17 '10 at 14:11

vector holding read-only matrices?

3 Answers3