Accessing std::vector data through pointer to first element.

As long as I am not inserting/erasing elements (or doing anything else
that may reallocate the memory) in the mean time, is it safe to assume
that the data in a vector is contiguous in memory and starts at
&(thevector[0])?

For example, say I have a vector of structures and I want to set it's
size to 100 then zero all the memory; can (not should) I do the
following:

vector<TheStructure> s;
s.resize(100);
memset(&(s[0]), 0, sizeof(TheStructure) * s.size());

And if I want to pass that info to, say, a function that normally
takes a plain old array of TheStructures, can I do this:

void function (TheStructure *data, unsigned);

function(&(s[0]), s.size());

It has worked in the past but is it something that's guaranteed about
a std::vector?

Thanks,
Jason