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?

kennytm · Accepted Answer · 2012-02-29 19:02:32Z

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, 2012 at 19:02

kennytm

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2 Comments

Lightness Races in Orbit Over a year ago

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.

Jeff Over a year ago

Just tried this, if you want no warnings, std::array<std::array<int, 2>, 2> shape = {{ {{1, 1}}, {{1, 1}} }};. eww

Basile Starynkevitch · Accepted Answer · 2012-02-29 17:53:51Z

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, 2012 at 17:53

Basile Starynkevitch

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2 Comments

Mihai Bişog Over a year ago

It works however I'm wondering why my version does not. Both expressions seem equivalent on a first look.

Lightness Races in Orbit Over a year ago

@zoopp: No they don't. Basile uses an explicit construction, whereas you do not.

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