Byte size used by std::vector

Question

I'm interfacing std::vector to a C program which needs to know the size in bytes.

Can I do this without the expression sizeof(vec[0]) ?

void *dest = get_dest();
std::vector<T> vec;
memcpy(dest, vec.data(), vec.size() * sizeof(vec[0]));

Please do not offer C++ style alternatives to memcpy .

Answer 1

template<class T, class A>
std::size_t bytes_in_vector( std::vector<T,A>const& v ){
  return v.size()*sizeof(T);
}
template<class A>
std::size_t bytes_in_vector( std::vector<bool,A> const& )=delete;

however, there is little wrong with sizeof(vec[0]) so long as T is not bool . If T is bool you are not allowed to use memcpy .