stack - How can you print an item that is void** data in C? -

When trying to make a test rig for the C stack I ran into problems in a way to display it correctly. I have checked six books and they have a way to push and pop from the stack, but do not give any examples how you actually use the routine. Can someone show me the pattern, so can I write a debug print statement?

The call to pop uses this structure:

  {struct element * next; Zero * data; }   
 The pop function is:  
  int pop (tElement ** stack, zero ** data)   
 How do I print data items?   
 
 
 You can print indicator value:  
  zero print_data ( Zero ** data) {printf ("% p", data); If (data) printf (", *% p", * data); }   
 Or, you can provide callback hooks to the user of the data structure to provide a print job for you:  
  zero pretty_print_data (zero) * * Data, zero (* print_callback) (zero **)) {printf ("% p% s", data, (data? "": ":")); If (data) printf (", *% p:", * data); If (print_callback) print_callback (data); }   
 The programmer providing callback knows what type of  data should be :  
  void print_point (zero ** Data) {if (data & amp; data) {point * p = * data; Printf ("(% d,% d)", p-> gt; x, p-> y); } Other {printf ("zero"); }}