title: how to get doxygen to produce call & caller graphs for c functions
body: <p>I've spent some time reviewing the docs and going through my doxy config file from end to end.  I cut doxygen loose on my config file and it produces documentation and indices for structs and cpp classes but I don't see call or caller graphs for the multitude of c functions in my source tree.</p>
  
  <p>Can anybody tell me how to configure doxygen to produces these call and caller trees ?  I do have graphviz installed.</p>