Initialize aggregate as class member

Question

In this code:

#include <array>
#include <cstdint>

struct K {
    std::array<char, 4> a;
    std::uint8_t b;
};

const K k1 = { {'T', 'e', 's', 't'}, 1 };

class X {
    const K k2 = { {'A', 'b', 'c', 'd'}, 2 };
};

I can initialize a global object k1 just fine. But trying to use the same syntax on a default initializer of the class member k2 gives compiler errors (similar errors from g++-4.8.2 and g++-5.2.0):

main.cpp:12:44: error: array must be initialized with a brace-enclosed initializer
     const K k2 = { {'A', 'b', 'c', 'd'}, 2 };
                                            ^
main.cpp:12:44: error: too many initializers for 'std::array<char, 4ul>'

What's the correct way to initialize k2 at its declaration?

Clang accepts it with warning `main.cpp:9:17: warning: suggest braces around initialization of subobject [-Wmissing-braces]` (for `std::array` initialization). — Jarod42, Dec 21 '15 at 21:38
[When can outer braces be omitted in an initializer list?](http://stackoverflow.com/questions/11734861/when-can-outer-braces-be-omitted-in-an-initializer-list) — M.M, Dec 21 '15 at 21:58

score 2 · Accepted Answer · answered Dec 21 '15 at 21:34

2

You just need an extra pair of braces:

class X {
    const K k2 = { {{'A', 'b', 'c', 'd'}}, 2 };
};

answered Dec 21 '15 at 21:34

101010

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I find it amusing that uniform initialisation is no such thing. – Lightness Races in Orbit Dec 21 '15 at 21:47
@LightnessRacesinOrbit More fun on the way, hold on for C++17 :) – 101010 Dec 21 '15 at 21:57
Is this a Standard requirement, or is g++ bugged to not accept the original? – M.M Dec 21 '15 at 22:00
@M.M I think that this was a requirement until C++14. I'm not aware if GCC conforms on this matter or not. – 101010 Dec 21 '15 at 22:03

Initialize aggregate as class member

1 Answers1