&something gives you the address of the std::vector object, not the address of the data it holds. &something.begin() gives you the address of the iterator returned by begin() (as the compiler warns, this is not technically allowed because something.begin() is an rvalue expression, so its address cannot be taken).
Assuming the container has at least one element in it, you need to get the address of the initial element of the container, which you can get via
&something[0] or &something.front() (the address of the element at index 0), or
&*something.begin() (the address of the element pointed to by the iterator returned by begin()).
In C++11, a new member function was added to std::vector: data(). This member function returns the address of the initial element in the container, just like &something.front(). The advantage of this member function is that it is okay to call it even if the container is empty.