Arrays and Vectors in

About Arrays and Vectors

Arrays and Vectors

C++ offers different containers to store elements of the same type in an ordered way. There is std::array for containers of a fixed size and std::vector, which comes with dynamic resizing capabilities.

Construction

When you declare an array or a vector you need to specify the type of elements, that container will hold. Arrays also need a size. Look at these examples to see the two container types' initializations:

#include<array>
#include <string>

// std::array variable_name<element_type, size> {list of elements}
std::array<std::string, 3> indie_rock {"yeah", "yeah", "yeah"};
// indie_rock contains the elements "yeah" three times

Vectors usually need more space, as they allocate memory for further growth. You do not need to specify a size:

#include<vector>

// std::vector variable_name<element_type> {list of elements}
std::vector countdown<int> {3, 2, 1};
// my_vector contains the elements 3, 2 and 1

Note: You do not need to know the exact mechanics behind the template concept yet, it will have its own concept further down the syllabus tree.

Element access

Vectors and arrays share the same functions to access their elements. You can use the member functions front and back to get the first and last elements of the container. There is also at and the [] operator to access speficic elements.

countdown[0];
// => 3
countdown.at(2);
// => 1
countdown[1] = 4;
// countdown now contains 3, 4 and 1
indie_rock.back() = "yeahs"; 
// indie_rock is now "yeah", "yeah", "yeahs"

Note: If you pick a position that is not in the range of your container, [] might lead to undefined behavior. The at function would raise an exception, which might make your life easier in the long term.

Vector modifiers

As a vector is not fixed in size, it is possible to add or remove elements. Two common functions for that purpose are emplace_back and pop_back.

std::vector<std::string> witches {"Holly", "Alyssa", "Shannen"};
witches.pop_back(); 
// Shannen is no longer with the witches
witches.emplace_back("Rose");
// Rose has joined the team

Capacity

You can check the containers for emptiness with the member function empty. If you want to know the number of elements, you can use size.