detecting timeout from waitForMessage

edit

Hi,

I'm using the waitForMessage function and can't seem to be able to find a way of detecting if the function has timed out.

Here's the code I have:

sensor_msgs::PointCloud2 pc;
pc  = *(ros::topic::waitForMessage<sensor_msgs::PointCloud2>(rgb_topic_, ros::Duration(10)));

How can I check and see if pc is valid?

If I try to read the fields of pc when it has timed out, the code exits with the following error:

calibration_executive: /usr/include/boost/smart_ptr/shared_ptr.hpp:412: boost::shared_ptr<T>::reference boost::shared_ptr<T>::operator*() const [with T = const sensor_msgs::PointCloud2_<std::allocator<void> >, boost::shared_ptr<T>::reference = const sensor_msgs::PointCloud2_<std::allocator<void> >&]: Assertion `px != 0' failed.
Aborted

By the way, the code is from the pr2_led_kinect_calib package.

Thanks.

------------------- update ------------------

Tried putting it in a try catch block but it didn't work

    try
    {
        pc  = *(ros::topic::waitForMessage<sensor_msgs::PointCloud2>(rgb_topic_, ros::Duration(10)));
        if ((after == ros::Time(0,0)) || (pc.header.stamp > after))
        {
            found = true;
        }   

    }
    catch (std::exception e)
    {
        ROS_ERROR("No point clound messages received in topic %s after waiting for %f seconds.", rgb_topic_.c_str(), waitTime);
        continue;
    }

It aborts at

    if ((after == ros::Time(0,0)) || (pc.header.stamp > after))

and no exception is thrown.

Also tried

if (!pc)

But pc is not a pointer so it gives a type mismatch compilation error.

------------------- update ------------------

Thanks for the responses!

As suggested, I tried storing the returned value as a shared pointer, then checking to see if it's NULL, and that worked.

boost::shared_ptr<sensor_msgs::PointCloud2 const> sharedPtr;
sensor_msgs::PointCloud2 pc;

sharedPtr  = ros::topic::waitForMessage<sensor_msgs::PointCloud2>(rgb_topic_, ros::Duration(10));
    if (sharedPtr == NULL)
        ROS_INFO("No point clound messages received);
    else
        pc = *sharedPtr;