CODEWITHSUNDEEP
c++c++11constexpr
mewo1234
mewo1234

Reputation: 319

can I declare a static array with constexpr function

// since we can dedfine a static array like this
int a[5] = {0};
// decltype(a[5]) is `int [5]`

// Then how about this way?
constexpr int sum(int a, int b) { return a + b; }
int a, b;
std::cin >> a >> b;
int arr[sum(a, b)] = {0};

it can be compiled successfully, but is arr a static array? when I tried to print arr type with typeid().name() or boost::typeindex::type_id_with_cvr, I got below error:

error: cannot create type information for type 'int [(<anonymous> + 1)]' because it involves types of variable size
 std::cout << typeid(decltype(arr)).name() << std::endl;

Upvotes: 2

Views: 225

Answers (1)

Alan Birtles
Alan Birtles

Reputation: 36379

As the value of a and b are not known at compile time the result of sum is not a constexpr.

The code compiles presumably because you are using GCC which has an extension which allows declaring arrays on the stack with variable size, standard c++ doesn't allow this.

Upvotes: 6

Related Questions