c - Inconsistent gcc diagnostic for string initialization

Question

I'm using gcc 4.9.1/Mingw and compiling the code with:

gcc test.c -otest.exe -std=c11 -pedantic-errors -Wall -Wextra

This code gives a diagnostic:

int main (void)
{
  char a[5] = {'h','e','l','l','o',''};
}

error: excess elements in array initializer char a[5]

However, this code does not yield a warning:

int main (void)
{
  char b[5] = "hello";
}

I thought the two forms were 100% equivalent. Is there any reason or subtlety in the C standard etc why the latter should not give a warning?

Or is this a compiler bug? I know that the C standard allows excess initializers, unlike C++, so formally I don't believe gcc is required to give a diagnostic. But I would expect the compiler to give warnings consistently.

Answer 1

While:

 char a[5] = {'h','e','l','l','o',''};

is invalid.

(C11, 6.7.9p2) "No initializer shall attempt to provide a value for an object not contained within the entity being initialized."

This:

char b[5] = "hello";

is explicitly allowed by C (emphasis mine):

(C11, 6.7.9p14) "An array of character type may be initialized by a character string literal or UTF?8 string literal, optionally enclosed in braces. Successive bytes of the string literal (including the terminating null character if there is room or if the array is of unknown size) initialize the elements of the array."

But

 char b[5] = "hello!";

is invalid.