OpenCL编程：创建设备结构cl_device_id

OpenCL程序中的设备用cl_device_id结构来表示。在向设备发送内核之前，需要调用clGetDeviceIDs创建一个cl_device_id。

函数原型如下：

cl_int clGetDeviceIDs(cl_platform_id platform, cl_device_type device_type, cl_uint num_entries, cl_device_id *devices, cl_uint *num_devices);

cl_device_id *devices;
cl_uint num_devices;

err = clGetDeviceIDs(platforms[0], CL_DEVICE_TYPE_ALL, 1, NULL, &num_devices);
if (err < 0)
{
	cout << "Couldn't find any devices." << endl;
	return err;
}
devices = (cl_device_id *)malloc(sizeof(cl_device_id) * num_devices);
err = clGetDeviceIDs(platforms[0], CL_DEVICE_TYPE_ALL, num_devices, devices, NULL);
if (err < 0)
{
	cout << "Failed to initialize devices." << endl;
	return err;
}