Introduction to Containers and Arrays

Introduction to Containers and Arrays

What is a container?

A container is an object that holds other objects - a collection of values stored together. Containers let you add items, count them, read them by index, and walk through them. There are many kinds; the one we start with is the array.

Arrays: the first container

An array is a container that stores several objects of the same type in a row in memory. It's the classic base container: simple, fast, and the foundation for many others.

C++ gives you two families of arrays:

• Built-in (C-style) arrays like int arr[3]. Fixed size decided at compile time, and little else - no self-knowledge of size, no bounds checks.
• Library arrays like std::vector, which wrap the idea with convenience: they know their size, check bounds, and grow automatically.

std::vector vs built-in arrays

std::vector is the modern workhorse: its size can change while the program runs, and it keeps track of how many elements it has. A built-in array is stuck at the size you declared, and it can decay into a pointer when passed around (more on that later).

The modern rule

In almost all new C++ code, reach for std::vector (dynamic) or std::array (fixed size) instead of raw built-in arrays. Built-in arrays still exist and still work, but the library types are safer and just as fast.

TL;DR

• A container is an object that holds other objects.
• Arrays are the base container of C++: same-type values in a row.
• Built-in arrays have a fixed compile-time size and little help.
• std::vector knows its size and can grow and shrink.
• Prefer std::array / std::vector over raw built-in arrays.