You can do that using at. You can try out the following simple example:
const size_t N = 20;
std::vector<int> vec(N);
try {
vec.at(N - 1) = 7;
} catch (std::out_of_range ex) {
std::cout << ex.what() << std::endl;
}
assert(vec.at(N - 1) == 7);
Notice that method at returns an allocator_type::reference, which is that case is a int&. Using at is equivalent to assigning values like vec[i]=....
There is a difference between at and insert as it can be understood with the following example:
const size_t N = 8;
std::vector<int> vec(N);
for (size_t i = 0; i<5; i++){
vec[i] = i + 1;
}
vec.insert(vec.begin()+2, 10);
If we now print out vec we will get:
1 2 10 3 4 5 0 0 0
If, instead, we did vec.at(2) = 10, or vec[2]=10, we would get
1 2 10 4 5 0 0 0