缺少C变量声明

Question

I came across the following code, I don't understand how this variable "win" works here without declaration?

//The following code is in a header file
static inline void Win_unlink(list_t * list, Win * shm_win)
{
    SHM_Win_t *elem = NULL;
    SHM_Win_t *tmp_elem = NULL;

    SEARCH_SCALAR(*list, elem, win, shm_win);
    if (elem != NULL) {
        tmp_elem = elem;
        MPL_DL_DELETE(*list, elem);
        MPL_free(tmp_elem);
    }
}

#define SEARCH_SCALAR(head,out,field,val) SEARCH_SCALAR_N(head,out,field,val,next)
#define SEARCH_SCALAR_N(head,out,field,val,_next)                                       \
do {                                                                                           \
    FOREACH_N(head,out,_next) {                                                         \
      if ((out)->field == (val)) break;                                                        \
    }                                                                                          \
} while(0)

I looked at the included header files, but there is no variable declared as "win". I also looked at the places where this function is called, I didn't find the declaration for "win" either. I used cscope to look for global definition of win, but I didn't see it.

Answer 1

Looking at the definition of SEARCH_SCALAR and SEARCH_SCALAR_N , it seems to me that win is not an independent variable. It represents a field/member of a struct .

  if ((out)->field == (val)) break;
             ^^^^ that's win in your use.