initialise a C++ std::array of struct in C++11

Question

I've read the similar questions, but does anyone know why if I have a struct

struct ArabicRoman {
    char roman;
    int arabic;
};

I can initialise a C++ std::array in the following way:

ArabicRoman M({'M', 1000});
ArabicRoman D({'D', 500});
array<ArabicRoman, 2> const SYMBOLS({ M, D });

I can initialise a C-style array in the following way:

ArabicRoman const SYMBOLS[]({ {'M', 1000}, {'D', 500} });

However, the following is not compiling:

array<ArabicRoman, 2> const SYMBOLS({ {'M', 1000}, {'D', 500} });

any workaround to initialise C++ style arrays of structs?

You need more braces.

Dimitrios Bouzas
– Dimitrios Bouzas

2015-11-07 18:36:14 +00:00
Commented Nov 7, 2015 at 18:36 — Dimitrios Bouzas
– Dimitrios Bouzas, Commented Nov 7, 2015 at 18:36

Dimitrios Bouzas · Accepted Answer · 2015-11-07 18:39:48Z

19

You need to replaces parentheses with braces:

std::array<ArabicRoman, 2> const SYMBOLS {{ {'M', 1000}, {'D', 500} }};
                                         ^                           ^

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answered Nov 7, 2015 at 18:39

Dimitrios Bouzas

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2 Comments

stivlo Over a year ago

thanks! I saw now in the reference en.cppreference.com/w/cpp/container/array that this style of double brace initialisation is C++11 syntax, and won't be required any more in C++14

Marc Glisse Over a year ago

@stilvo It is true that you don't need double braces in simple cases, but with nested braces they can be hard to avoid...

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