Access Vector Elements Directly and Safely
Learn to access vector elements directly and safely.
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The vector is one of the most widely used containers in the STL, and for good reason. It's just as convenient as an array but far more powerful and flexible. It's common practice to use the [] operator to access elements in a vector like this:
vector v{ 19, 71, 47, 192, 4004 };auto & i = v[2];
The vector class also provides a member function for the same purpose:
auto & i = v.at(2);
The result is the same but there is an important difference. The at() function does bounds checking and the [] operator does not. This is intentional, as it allows the [] operator to maintain compatibility with the original C-array. Let's examine this in a bit more detail.
How to do it
There are two ways to access an element with an index in a vector. The at() member function does bounds checking, and the [] operator does not.
Here's a simple
main()function that initializes a vector and accesses an element:
int main() {vector v{ 19, 71, 47, 192, 4004 };auto & i = v[2];cout << format("element is {}\n", i);}
Output: ...