How do I best save a transform to a file?

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Since it seems the rosbag C++ API doesn't work very well with the tf library, and I cannot find a simple way of saving ROS datatypes to files, I don't know how to best save a transform that I have calculated. I really need something that maintains the datatype, so that I won't need to make my own functions just to separately read position and orientation and so forth.

For what it's worth, I am considering using just a geometry_msgs::Quaternion and a geometry_msgs::Point and recreating the transform from those data. Any other recommendations?