Is there a way of getting the size of an array without finding it manually?

Question

So ive been making arrays this way but i found a error, lets say it was a loop that copied and array element by element:

int v1[] = { 3, 4, 7, 8};
int v2[sizeof(v1)];
for (auto i = 0; i < sizeof(v2); ++i)
{
  v2[i] = v1[i]
}

The v2 array will not have the size of 4 integers, it adds them all up. So v2 would have the size of 22 not 4 integers. So i was wondering if there was any way of finding the size of an array without having to go to the array and see how many there elements there are manually. Is there a way? thanks.

Just change `sizeof(v1)` and `sizeof(v2)` to `sizeof(v1)/sizeof(int)` and `sizeof(v2)/sizeof(int)` or `sizeof(v1)/sizeof(v1[0])` and `sizeof(v2)/sizeof(v1[0])` — DimChtz, Apr 15 '16 at 00:22
sizeof(v1) returns total byte size of memory under array, not count of int's. — Ivan, Apr 15 '16 at 01:26

score 3 · Answer 1 · answered Apr 15 '16 at 00:13

3

Just use std::array or std::vector:

std::array<int, 4> v1 { 3, 4, 7, 8};
auto v2 = v1;

Live demo

answered Apr 15 '16 at 00:13

Shoe

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Thank you, should i always prefer std::array over the c style array – Harry the hacker Apr 15 '16 at 00:15
1

@Harrythehacker When in doubt, yes. It's pretty much superior in any possible way. – Shoe Apr 15 '16 at 00:15
In C++? Definitely, unless you are calling a C API that demands a C style array. – David Hoelzer Apr 15 '16 at 00:15
1

@DavidHoelzer Even then you can use [`data`](http://en.cppreference.com/w/cpp/container/array/data). – Shoe Apr 15 '16 at 00:16
@Harrythehacker Be sure to checkmark the answer that helped you most. ;) – Mateen Ulhaq Apr 15 '16 at 01:11

score 2 · Accepted Answer · edited Apr 15 '16 at 00:36

2

While I agree with the rest that you should use STL containers in general, in your case you can get the count of the elements in the array by using sizeof(v1)/sizeof(int). sizeof(v1) will give you the total number of bytes for a 4 integer array and dividing by sizeof(int) will give you the number of elements.

edited Apr 15 '16 at 00:36

Jarod42

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answered Apr 15 '16 at 00:23

overflowingstack

61
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Thank you for the formatting help. – overflowingstack Apr 15 '16 at 00:42
Although I'd still recommend using ````std::array````, this piece of code can be slightly improved by using ````sizeof(v1)/sizeof(decltype(v1))````. – Apr 15 '16 at 01:46

Is there a way of getting the size of an array without finding it manually?

2 Answers2