Something

#include <stdio.h>
int main() {
 int res;
 #if defined(HAVE_FDATASYNC)
  printf("fdatasync \n");
  res= fdatasync(fd);
 #elif defined(HAVE_FSYNC)
  printf("fsync \n");
  res= fsync(fd);
 #else
  printf("error \n");
  res= 0;                                     /* No sync (strange OS) */
 #endif
 return 0;
}