The following code works:

Code: Select all

double ptr1[9]={1,2,3,4,5,6,7,8,9};
const double ptr2[9]={1,2,3,4,5,6,7,8,9};
Map<Matrix<double,3,3> >    mUseless(ptr1);
new (&mUseless) Map<const Matrix<double,3,3> > (ptr2);
mUseless(1,1)=6.0;


why??

Calling placement new does not change the type of the object, and since mUseless is not a const Map, it is perfectly normal that you can change the object. Your code is similar to a reinterpret_cast from a Map<const Matrix<double,3,3> > to a Map<Matrix<double,3,3> >.

So how may I protect a Map from writing?? I'm using the same map for several operatation with raw buffers. Some of
those buffers are const. It is mandatory to use specially a new Map<const Type > to work with const arrays? or there
is another way to implement a single map to work with both const and not const in a secure way??

And there is not a way to forbid the "new (&,mUseless) Map<const Matrix<double,3,3> >" statements when mUseless is
not a map to const??

You can use const map even to map non const pointers:

Map<const Matrix<double,3,3> > mUseless(ptr1);

In which case mUseless(1,1)= blabla; will be forbidden regardless of the constness of the input pointer. But in C++ an object cannot change its constness at runtime!