How do you initialize (through initializer lists) a multidimensional std::array in C++11?

Question

I am trying to initialize a 2D std::array trough initializer lists however the compiler tells me that there are too many initializers.

e.g.:

std::array<std::array<int, 2>, 2> shape = { {1, 1},
                                            {1, 1} };

Compiler error: error: too many initializers for ‘std::array<std::array<int, 2ul>, 2ul>’

But clearly there aren't too many. Am I doing something wrong?

score 14 · Accepted Answer · answered Feb 29 '12 at 19:02

14

Try to add one more pair {} to ensure we're initializing the internal C array.

std::array<std::array<int, 2>, 2> shape = {{ {1, 1},
                                             {1, 1} }};

Or just drop all the brackets.

std::array<std::array<int, 2>, 2> shape = { 1, 1,
                                            1, 1 };

answered Feb 29 '12 at 19:02

kennytm

It always feels like an abstraction leak to me that we have to do that. Just a result of the library not being "internal" to the language, but built _with_ it, I suppose. – Lightness Races in Orbit Mar 08 '12 at 13:30
1

Just tried this, if you want no warnings, `std::array, 2> shape = {{ {{1, 1}}, {{1, 1}} }};`. eww – Jeff Sep 29 '12 at 03:37

score 7 · Answer 2 · answered Feb 29 '12 at 17:53

7

I would suggest (without even have trying it, so I could be wrong)

typedef std::array<int, 2> row;
std::array<row,2> shape = { row {1,1}, row {1,1} };

answered Feb 29 '12 at 17:53

1

It works however I'm wondering why my version does not. Both expressions seem equivalent on a first look. – Mihai Bişog Feb 29 '12 at 19:25
@zoopp: No they don't. Basile uses an explicit construction, whereas you do not. – Lightness Races in Orbit Mar 08 '12 at 13:30

2 Answers2