Create a function pointer which takes a function pointer as an argument

Question

I'm trying to create a function pointer that takes a function pointer as an argument, but am not sure how to go about it... I was advised to try typedef-ing one of my function pointers, but get the same error. Could someone help me with the correct syntax?

    int
186 main(int argc, char **argv)
187 {
188   int             i;

194   typedef int   (*search_alg) (int *, int, int);
195   typedef int   (*search) (search_alg);
196   set_t         (*intersect_alg) (list_t *, (search));
197
198   clo_t          *iopts = parse_args(argc, argv);
199
200   /* select interstion algorithm */
201   switch (iopts->imode) {
202   case SVS:
203     fprintf(stdout, "ALGORITHM : SvS\n");
204     intersect_alg = svs;
205     break;
206   case SEQ:
207     fprintf(stdout, "ALGORITHM : Sequential\n");
208     intersect_alg = sequential;
209     break;
210   case ADP:
211     fprintf(stdout, "ALGORITHM : Adaptive\n");
212     intersect_alg = adaptive;
213     break;
214   default:
215     fprintf(stdout, "ALGORITHM : Unknown\n");
216     return (EXIT_FAILURE);
217   }
218
219   /* select fsearch algorithm */
220   switch (iopts->mode) {
221   case LIN:
222     fprintf(stdout, "F-SEARCH : Linear\n");
223     search = linear_fsearch;
224     break;
225   case BIN:
226     fprintf(stdout, "F-SEARCH : Binary\n");
227     search = binary_fsearch;
228     break;
229   case INP:
230     fprintf(stdout, "F-SEARCH : Interpolation\n");
231     search = interpolation_fsearch;
232     break;
233   case EXP:
234     fprintf(stdout, "F-SEARCH : Exponential\n");
235     search = exponential_fsearch;
236     break;
237   default:
238     fprintf(stdout, "F-SEARCH : Unknown\n");
239     return (EXIT_FAILURE);
240   }
241

244
245   /* perform intersection and run timings */
246   for (i = 0; i < iopts->runs; i++) {
248     /* perform intersect search */
249     intersect_alg (iopts->data_files, search);
252   }

The line I'm trying to make work is 249, I originally tried

int (*search_alg) (int *, int, int);
set_t (*intersect_alg) (list_t *, (*) (int *, int, int);

and would probably prefer to do it that way if possible. The error I'm getting is:

main.c:204: warning: assignment from incompatible pointer type
main.c:208: warning: assignment from incompatible pointer type
main.c:212: warning: assignment from incompatible pointer type

And the functions I'm pointing to are:

     22   /** Finger Search Operations for array sets **/
 23   int             linear_fsearch(int *set, int len, int key);
 24   int             binary_fsearch(int *set, int len, int key);
 25   int             interpolation_fsearch(int *set, int len, int key);
 26   int             exponential_fsearch(int *set, int len, int key);
 27
 28   /** Intersect Algorithms **/
 29   set_t          *svs(list_t * list, int (*srch_alg) (int *, int, int));
 30   set_t          *sequential(list_t * list, int (*srch_alg) (int *, int, int    ));
 31   set_t          *adaptive(list_t * list, int (*srch_alg) (int *, int, int));

Can anyone see what I'm doing wrong? I can't figure it out. Thanks!

Rhys.

Answer 1

The declaration you need for intersect_alg is

set_t *(*intersect_alg)(list_t *, int (*)(int *, int, int));