STL container assignment and const pointers

Question

This compiles:

int* p1;
const int* p2;
p2 = p1;

This does not:

vector<int*> v1;
vector<const int*> v2;
v2 = v1;  // Error!
v2 = static_cast<vector<const int*> >(v1);  // Error!

What are the type equivalence rules for nested const pointers? I thought the conversion would be implicit. Besides, I'd rather not implement point-wise assignment of STL containers, unless I really have to.

Answer 1

Direct assignment is not possible. As others explained, the equivalence is not established by the pointer types, but by the container types. In this case, vector doesn't want to accept another vector that has a different, but compatible element type.

No real problem, since you can use the assign member function:

v2.assign(v1.begin(), v1.end());

Answer 2

Conversion from int* to const int* is built into the language, but vectors of these have no automatic conversion from one to the other.