How to call a pointer function in a structure?

Question

I am working with the xinu embedded system in c. I created a new header file and declared a structure:

struct callout {
   uint32 time;      /* Time of delay in ms */
   void *funcaddr;   /* Function pointer */
   void *argp;       /* Function arguments */
   uint32 cid;       /* Callout id for the specific callout */
   char *sample;

};

Basically, I am trying to declare a struct object and a funcaddr function for a function.

void test();

process main(void) {
   struct callout *coptr;

   coptr->sample ="hellowolrd";
   coptr->funcaddr = &test;

   (coptr->funcaddr)(coptr->argp);    //error here
   kprintf("coptr %s \n", coptr->sample);

   return OK;

 }

 void test() {
    kprintf("this is the test function \n");
 }

I try to call a function pointer through a structure, but I get an error: main.c: 30: 19: error: the called object is not a function or function pointer (Coptr-> funcaddr) ();

Please show what is the correct syntax for calling a function pointer.

Answer 1

You declared funcaddras a pointer to an object. To declare a pointer to a function, it looks like this:

struct callout {
   uint32 time;
   void (*funcaddr)();  // <-------- function pointer

Then the rest of your code should work.

---

coptr->funcaddr = &test;, , , .