8.3.4p4中的C ++ 11数组声明示例与gcc或clang不匹配？

Question

This is a subset of an example from C++11 (same through to latest draft) 8.3.4p4 ([dcl.array]/4):

extern int x[10];                   // 1

int x[]; // OK: bound is 10         // 2

void f() {
    extern int x[];                 // 3
    int i = sizeof(x); // error incomplete type
}

gcc does not agree with the error and gives:

error: type mismatch with previous external decl of ‘int x []’

instead (at declaration 3).

clang compiles without error.

My intepretation would be that the example is well-formed. Declaration 3 should link to declaration 1 and 2, and should therefore have type array of 10 int , and not array of unknown bound int . So it should be complete at the sizeof.

Who is correct? The standard, gcc or clang?

Answer 1

8.3.4/3 includes:

Furthermore, if there is a preceding declaration of the entity in the same scope in which the bound was specified, an omitted array bound is taken to be the same as in that earlier declaration,

Since the declaration inside the function is not in the same scope as the global declaration that doesn't apply, and therefore does not grant permission to omit the array bound. I don't see any other text that would permit the omission either, and therefore the type of x in the sizeof(x) expression is incomplete.

Clang should not be accepting the code, gcc is rejecting it for the wrong reason, and the standard's example looks accurate to me.