The hello world example gives a simple application that prints the name of the default compute device on the system.

The boost::compute::system class provides access to the OpenCL platforms and devices present on the host system.

Compute devices are represented with the device class.

#include <iostream>

#include <boost/compute/core.hpp>

namespace compute = boost::compute;

int main()
{
    // get the default device
    compute::device device = compute::system::default_device();

    // print the device's name
    std::cout << "hello from " << device.name() << std::endl;

    return 0;
}

Before any computation occurs, data must be transferred from the host to the compute device. The generic copy() function provides a simple interface for transfering data and the generic vector<T> class provides a container for storing data on a compute device.

The following example shows how to transfer data from an array on the host to a vector<T> on the device and then back to a separate std::vector<T> on the host. At the end of the example both host_array and host_vector contain the same values which were copied through the memory on the compute device.

#include <vector>

#include <boost/compute/algorithm/copy.hpp>
#include <boost/compute/container/vector.hpp>

namespace compute = boost::compute;

int main()
{
    // get default device and setup context
    compute::device device = compute::system::default_device();
    compute::context context(device);
    compute::command_queue queue(context, device);

    // create data array on host
    int host_data[] = { 1, 3, 5, 7, 9 };

    // create vector on device
    compute::vector<int> device_vector(5, context);

    // copy from host to device
    compute::copy(
        host_data, host_data + 5, device_vector.begin(), queue
    );

    // create vector on host
    std::vector<int> host_vector(5);

    // copy data back to host
    compute::copy(
        device_vector.begin(), device_vector.end(), host_vector.begin(), queue
    );

    return 0;
}

The following example shows how to calculate the square-root of a vector of floats on a compute device using the transform() function.

#include <vector>
#include <algorithm>

#include <boost/compute/algorithm/transform.hpp>
#include <boost/compute/container/vector.hpp>
#include <boost/compute/functional/math.hpp>

namespace compute = boost::compute;

int main()
{
    // get default device and setup context
    compute::device device = compute::system::default_device();
    compute::context context(device);
    compute::command_queue queue(context, device);

    // generate random data on the host
    std::vector<float> host_vector(10000);
    std::generate(host_vector.begin(), host_vector.end(), rand);

    // create a vector on the device
    compute::vector<float> device_vector(host_vector.size(), context);

    // transfer data from the host to the device
    compute::copy(
        host_vector.begin(), host_vector.end(), device_vector.begin(), queue
    );

    // calculate the square-root of each element in-place
    compute::transform(
        device_vector.begin(),
        device_vector.end(),
        device_vector.begin(),
        compute::sqrt<float>(),
        queue
    );

    // copy values back to the host
    compute::copy(
        device_vector.begin(), device_vector.end(), host_vector.begin(), queue
    );

    return 0;
}