What is the difference between a vector and an array in C++?
A raw array has a fixed size set at compile time and does not know its own length. A std vector is a dynamic array that can grow and shrink at run time, tracks its size, and manages its own memory. Vectors are safer and more flexible, so they are the default choice, while raw arrays are used only for simple fixed size or low level cases.
- A raw array has a fixed compile time size and does not track its own length.
- A std vector is a dynamic array that resizes, tracks its size, and manages its memory.
- Prefer vector by default and use raw arrays only for small fixed cases.
Quick comparison
- Size: array is fixed, vector can resize at run time.
- Memory: array is manual, vector manages its own.
- Safety: vector knows its size and offers bounds checked access with at().
- Use: vector by default, raw array for small fixed cases.
#include <vector>
std::vector<int> v;
v.push_back(1); // grows automatically
int arr[3] = {1,2,3}; // fixed size, cannot growSay prefer std vector in modern C++ because it manages memory and size for you, and use raw arrays only when you must. That practical stance matches how experienced C++ developers actually code.
Frequently asked questions
How does a vector grow when it runs out of space?
It allocates a larger block, usually doubling capacity, copies or moves the elements over, and frees the old block, giving amortised O(1) appends.
What is the difference between at() and the index operator?
at() checks bounds and throws an exception if the index is invalid, while the index operator does not check and gives undefined behaviour out of range.
Common follow up questions
Related interview questions
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