Is it legal in C++17 to declare an array of size 0?

Question

int main()
{
    int n[0];   
}

The code above is ok with Clang 4.0.

However, http://en.cppreference.com/w/cpp/language/array says:

The size of an array must be a value greater than zero.

Is it legal to declare an array of size 0 as per the C++17 standard?

see [What is the use of 0-length array (or std::array)?](http://stackoverflow.com/q/26209190/1708801) — Shafik Yaghmour, Apr 13 '17 at 16:22
[More warnings.](https://wandbox.org/permlink/EgXzQkeKoGQhdvVK) When it comes to whether something is standard or an extension, `-pedantic` is the appropriate flag. — chris, Apr 13 '17 at 16:23

score 11 · Accepted Answer · edited Jun 20 '20 at 09:12

Is it legal to declare an array of size 0 as per the C++17 standard?

No, nothing has changed in C++17 to allow zero sized arrays. Per the C++17 draft [dcl.array]/1

In a declaration T D where D has the form

D1 [ constant-expression_opt] attribute-specifier-seq_opt

[...]If the constant-expression is present, it shall be a converted constant expression of type std::size_t and its value shall be greater than zero.[...]

^{emphasis mine}

What you are seeing here is a non standard compiler extension that is allowing you to compile the code.

You can disable these extensions by using the -pedantic compiler flag.

score 3 · Answer 2 · answered Apr 13 '17 at 16:25

3

It's "legal" only because it's an extension of gcc and clang. If you compile with -pedantic then you'll see that what you're doing is not working with the ISO C++ Standard

answered Apr 13 '17 at 16:25

Andria

4,712
2
22
38

Is it legal in C++17 to declare an array of size 0?

2 Answers2