//example 1, do sth to all elements in vector using c-style API
void doSomething(const int *pInts, size_t numlnts);

vector<int> v;
if (!v.empty()) {
    doSomething(&v[0], v.size());
}

//example 2, init vector with c-style API
size_t fillArray(double *pArray, size_t arraySize);

vector<double> vd(maxNumDoubles);
vd.resize(fillArray(&vd[0], vd.size()));