Replace an element into a specific position of a vector
vec1[i] = vec2[i]
will set the value of vec1[i]
to the value of vec2[i]
. Nothing is inserted. Your second approach is almost correct. Instead of +i+1
you need just +i
v1.insert(v1.begin()+i, v2[i])
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