Using a C pointer in Guile

[Brian McAndrews]

I want to have the ability to pass a C pointer to guile.  I then want to
modify the data structure pointed to by the pointer such that those changes
are reflected back on the C side of things.  For example, if I had a data
structure that contained information about an automobile (ie,
number_of_doors, gas_mileage, weight...), but I wanted to review that data
structure in guile, and change one of the parameters.  How would I do that?
Is that what smobs are for?

Thanks,
Brian