How can I insert element into beginning of vector?
I need to insert values into the beginning of a std::vector
and I need other values in this vector to be pushed to further positions for example: something added to beginning of a vector and values moved from position 1 to 2, from 2 to 3 etc.
How can I do that?
Use the std::vector::insert function accepting an iterator to the first element as a target position (iterator before which to insert the element):
#include <vector>
int main() {
std::vector<int> v{ 1, 2, 3, 4, 5 };
v.insert(v.begin(), 6);
}
Alternatively, append the element and perform the rotation to the right:
#include <vector>
#include <algorithm>
int main() {
std::vector<int> v{ 1, 2, 3, 4, 5 };
v.push_back(6);
std::rotate(v.rbegin(), v.rbegin() + 1, v.rend());
}
You should consider using std::deque
. It works alot like a std::vector
but you can add and remove items from both the front and the end.
It does this by dividing the internal storage up into smaller blocks. You still have random-access iterators with good lookup speed.
If your container is small it should be fine to use the std::vector
approach but if you are storing large amounts of data the std::deque
s performance for inserting/deleting at the front will be far superior.