How to initialize std::array in class definition?

Question

Since C++11, it is possible to initialize member variables in class definitions:

class Foo {
   int i = 3;
}

I know I can initialize an std::array like this:

std::array<float, 3> phis = {1, 2, 3};

How can I do this in a class definition? The following code gives an error:

class Foo {
    std::array<float, 3> phis = {1, 2, 3};
}

GCC 4.9.1:

error: array must be initialized with a brace-enclosed initializer 
std::array<float, 3> phis = {1, 2, 3};
                                     ^ error: too many initializers for 'std::array<float, 3ul>'

Cory Kramer · Accepted Answer · 2014-10-02 13:00:15Z

3

You need one more set of braces, which is non-intuitive.

std::array<float, 3> phis = {{1, 2, 3}};

answered Oct 2, 2014 at 13:00

Cory Kramer

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2 Comments

juanchopanza Over a year ago

This doesn't explain why you can say std::array<float, 3> phis = {1, 2, 3}; outside of a class definition. I would have expected brace elision to apply here too (but I'm usually wrong about this one.)

Cory Kramer Over a year ago

@juanchopanza I think you are correct as far as the standard is concerned, see the comments in this thread. You should be able to use a single set of braces, it is an issue with GCC that is being addressed (AFAIK)

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