Can a struct of doubles be typecast to an array of doubles in C?

Question

Is this legal in C?

struct Doubles
{
  double a,b,c;
};

void foo(struct Doubles* bar)
{
  double* baz = (double*)bar;
  baz[0]++;
  baz[1]++;
  baz[2]++;
}

I know that it "works" on MSVC 2010, but I don't know if it's legal, or if different layouts could cause UB.

Answer 1

This leads to undefined behaviour. The layout of the struct is not totally prescribed by the standard. For instance, there may be padding.