How to properly define a function pointer in struct, which takes struct as a pointer?

Question

I have a struct with a callback function, the callback function needs a pointer to the structure in order to do its operation. How do I properly define these elements such t

Answer 1

There are two ways to do it — for both your example structures. They are essentially isomorphic.

1. Use a structure tag, as already shown in various other answers.

   typedef struct pr_PendingResponseItem
   {
       // some fields required for processing...
       int (*doAction)(struct pr_PendingResponseItem *pr);
   } pr_PendingResponseItem;
   
   typedef struct LinkedItem
   {
       struct LinkedItem *prev;
       struct LinkedItem *next;
       void * data;
   } LinkedItem;
   

2. Use typedef to give a name to an incomplete structure type and use the typedef in the structure definition.

   typedef struct pr_PendingResponseItem pr_PendingResponseItem;
   struct pr_PendingResponseItem
   {
       // some fields required for processing...
       int (*doAction)(pr_PendingResponseItem *pr);
   };
   
   typedef struct LinkedItem LinkedItem;
   struct LinkedItem
   {
       LinkedItem *prev;
       LinkedItem *next;
       void * data;
   };
   

Note that the structure tags are in a different namespace from the typedef names, so there is no need to use different names for the typedef and structure tag. Also note that in C++ the typedef would be unnecessary.