Is it safe to pass a vector as an array?

Question

Say I have a function:

void someFunc(int *x,int count);

which is out of my control, so I can't write it to accept iterators.

Is it safe to call it like so (regardless of the specific STL implementation):

vector<int> v;
/* ... */
someFunc(&v[0],v.size());

Obviously, one counter example is vector<bool>. How about any other type? (assuming I haven't specialized vector in any way).

Answer 1

Yes. Assuming v.size() > 0, this is safe (If the vector is empty, then v[0] results in undefined behavior).

The elements of a std::vector container are stored contiguously, just like in an ordinary array.

Answer 2

From section 23.2.4, point 1 of the standard:

[...] The elements of a vector are stored contiguously, meaning that if v is a vector where T is some type other than bool, then it obeys the identity &v[n] == &v[0] + n for all 0 <= n < v.size().

So yes, it is safe.

Note: If v is empty v[0] is undefined behavior so you should only do this if v is not empty.