C++:How to have an array of boost::multi_array

Question

Hi I have a few boost::multi_array defined as below:

typedef boost::multi_array<double, 3> region_prior_integral_image

I am trying to create an array of region_prior_integral_image like the following:

unordered_map<string, int> filename_to_hash_key_map = get_filename_to_hash_key_map();

unordered_map<string, region_prior_integral_image> filename_to_region_prior_map = get_region_prior_integral_images();

region_prior_integral_image* image_cache = new region_prior_integral_image[5];
for(unordered_map<string, int>::iterator it = filename_to_hash_key_map.begin(); it != filename_to_hash_key_map.end(); it++){
    image_cache[it->second] = filename_to_region_prior_map[it->first];
}

However the program is terminating with the following: SemanticTextonForest: /home/aly/libs/boost_1_51_0/stage/include/boost/multi_array/multi_array_ref.hpp:488: boost::multi_array_ref<T, NumDims>& boost::multi_array_ref<T, NumDims>::operator=(const ConstMultiArray&) [with ConstMultiArray = boost::multi_array<double, 3ul>, T = double, long unsigned int NumDims = 3ul, boost::multi_array_ref<T, NumDims> = boost::multi_array_ref<double, 3ul>]: Assertionstd::equal(other.shape(),other.shape()+this->num_dimensions(), this->shape())' failed.`

And I have no idea why?

I know I could just use a vector, but for arguments sake lets say I wanted to have an array of region_prior_integral_images

Thanks

Danqi Wang · Accepted Answer · 2012-11-13 10:33:13Z

1

Let's say we have two region_prior_integral_image instances: A and B. If you want to assign B to A, like A = B;, the shapes of A and B must be equal. The error message is saying that, in your code image_cache[it->second] = filename_to_region_prior_map[it->first];, the two arrays are of different shapes.

How do you created the arrays in filename_to_region_prior_map? I guess you used this constructor to specify the shapes: multi_array<double,3> B(boost::extents[i][j][k]). Hence their shape is [i][j][k]. But when you create the image_cache, the default constructor is invoked. So the two shapes mismatch.

My opinion is to store pointers of region_prior_integral_image in your code, which will save a lot of copy as well.

answered Nov 13, 2012 at 10:33

Danqi Wang

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4 Comments

Aly Over a year ago

any idea how to get the dimensions of an already created region_prior_image?

Danqi Wang Over a year ago

Use const size_type* shape() const; like: auto s = A.shape();, then u can access it by s[0], s[1] and s[2] in your case. Better read through the official reference: boost.org/doc/libs/1_52_0/libs/multi_array/doc/reference.html

Aly Over a year ago

How do I create the array of region_prior_images of a given size?

Danqi Wang Over a year ago

It is impossible. Only the default constructor will be invoked when using a primitive array. I suggest use std::vector instead, then u can use std::vector::resize(n, region_prior_image(boost::extents[i][j][k])) to fill it.

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