Thrust vector with custom data type

Question

I am using the thrust library for my project and ran into the following problem:

I have a struct called box defined as

typedef struct {
    int coord[4];
    float h;
} box;

and am now trying to copy data from a device_vector of boxes to a host_vector of boxes:

thrust::device_vector<box> d_boxes(100);
thrust::host_vector<box> h_boxes;
thrust::copy(d_boxes.begin(), d_boxes.end(), h_boxes.begin());

But this throws the error

terminate called after throwing an instance of 'thrust::system::system_error' what(): invalid argument

If I do the same with int instead of box, it works fine. Unfortunately, the documentation does not seem to have any example of vectors of custom data types.

What did I miss?

Answer 1

thrust::copy doesn't automatically resize vectors for you (actually no thrust algorithms do.)

So this is an empty vector, not large enough to hold 100 objects:

thrust::host_vector<box> h_boxes;

Try this instead:

thrust::host_vector<box> h_boxes(100);

As pointed out by @JaredHoberock, an alternate realization could be:

thrust::device_vector<box> d_boxes(100);
thrust::host_vector<box> h_boxes = d_boxes;

In this case, the constructor for h_boxes creates it with a size appropriate to hold the number of elements in d_boxes (as well as performing the device -> host data copy.)