When is it appropriate to use dynamic array as opposed to static array?

Question

Dynamic and static arrays: When both are possible, what's usually the rationale behind using one over the other?

One of the situations might be

int n;
cin >> n;
int a[n];

versus

int n;
cin >> n;
int* a = new int[n];

int a[n] is called variable length arrays, and is invalid, don't write them. — Passer By
– Passer By, Commented Oct 22, 2017 at 18:32
@HuXinqiao That's because compilers typically support not only standard C++, but also certain language extensions. When passed the right compiler flags (-pedantic/-pedantic-errors with GCC), such extensions will be warned about. — user743382
– user743382, Commented Oct 22, 2017 at 18:35
@HuXinqiao You're probably using gcc without warnings enabled. — melpomene
– melpomene, Commented Oct 22, 2017 at 18:38

gsamaras · Accepted Answer · 2017-10-22 18:38:04Z

1

int a[n] is a variable-length array, which is not allowed by the C++ standard, thus the second code snipper should be your option.

Use -pedantic flag, and you should get:

warning: ISO C++ forbids variable length array 'a' [-Wvla]
     int a[n];
            ^

answered Oct 22, 2017 at 18:38

gsamaras

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chessprogrammer · Accepted Answer · 2017-10-22 21:25:20Z

0

As other answers pointed out, you semantics of a variable length array is invalid. However, c++ does support dynamic length arrays via the Vector class, so your question still makes sense, just not with the syntax you used. I am going to interpret the question then as should you use Vectors or arrays. The answer is:

1)Use arrays when you don't need dynamic size or resizing and speed is critical and you are not concerned with the array index being out of bounds.

2)otherwise use vectors

answered Oct 22, 2017 at 21:25

chessprogrammer

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