indicating progress in RGui from a c function

I'd like to indicate progress of a calculation from within a C
shared library to the R GUI.  The apparent function call is
flush.console() after RPrintf, but it isn't clear to me what the
easiest way to do this is.  Would it be possible to add a flag to
RPrintf to have this done implicitly?

When you do get this sorted out, you may want to consider a verbose
option that toggles such updating of the GUI.  When users want to run
code in a non-interactive mode, such output can get in the way.

You could use interactive() to determine a default value for the
verbose option.

Best,

+ seth