C++: What is the difference between std::vector and std::array?

vector — dynamic size. array — fixed size.

std::vector:

• Dynamic size.
• Heap allocation.
• Can grow/shrink.
• Slightly more overhead.

1std::vector<int> v = {1, 2, 3};
2v.push_back(4);  // OK
3v.resize(10);    // OK

std::array (C++11):

• Fixed size (compile-time).
• Stack allocation.
• Size known at compile time.
• No overhead.

1std::array<int, 3> arr = {1, 2, 3};
2// arr.push_back(4);  // Error!
3arr[0] = 10;  // OK

When to use:

• vector — size unknown or changes.
• array — fixed size, performance critical.

Size:

1std::array<int, 5> arr;
2constexpr size_t size = arr.size();  // Compile-time