C++ 3D array declaration using vector

Question

I have some C++ code where I am declaring 2D arrays using "vector" with the following method:

    std::vector<std::vector<double>> Array2D(X, std::vector<double>Y);

where X and Y are the dimensions of the array.

This works beautifully for what I need to achieve. However I would like to look at using the same method for 3D, XYZ arrays. I assume I start with:

    std::vector<std::vector<std::vector<double>>>

but how do I declare the dimensions, ie Array3D(X, ?????)

Would you mind posting a minimal reproducible example please. — πάντα ῥεῖ
– πάντα ῥεῖ, Commented Oct 9, 2015 at 0:40
DON'T use such nested vectors to create 3D matrices. They are slow, since the memory is not guaranteed to be contiguous anymore and you'll get cache misses. Better use a flat vector and map from 3D to 1D and viceversa. — vsoftco
– vsoftco, Commented Oct 9, 2015 at 0:49
@Ahmetİnal (X,Y,Z) -> (X + Y * DX + Z * DY * DX), where DX and DY are the dimensions on X and Y, respectively — vsoftco
– vsoftco, Commented Oct 22, 2021 at 11:21

EvgeniyZh · Accepted Answer · 2015-10-09 00:45:55Z

7

There is fill vector constructor, which constructs a container with n elements, and each element is a copy of value provided.

std::vector<std::vector<std::vector<double>>> Array3D(X, std::vector<std::vector<double>>(Y, std::vector<double>(Z)));

will create X by Y by Z vector. You probably would like to use typedef for this type.

answered Oct 9, 2015 at 0:45

EvgeniyZh

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1 Comment

Fitzy Over a year ago

Legend. Spot On. That is exactly what I was after. Cheers

Community · Accepted Answer · 2017-05-23 11:54:00Z

3

You can declare like

 std::vector<std::vector<std::vector<double> > > Array3D(X, std::vector<std::vector<double> >(Y, std::vector<double>(Z)));

Where X, Y, Z are the dimension of 3D vector.

NB

It's better not to use 3D vector as mentioned by vsoftco

DON'T use such nested vectors to create 3D matrices. They are slow, since the memory is not guaranteed to be contiguous anymore and you'll get cache misses. Better use a flat vector and map from 3D to 1D and viceversa.

edited May 23, 2017 at 11:54

CommunityBot

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answered Oct 9, 2015 at 0:39

ashiquzzaman33

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