"Dereferencing pointer to incomplete type"，typedef 没问题

Question

我正在尝试实现哈希 table。我收到上述错误，但 AFAIK 我已经正确声明了我所有的 structs/typedefs。（我还在学C，sorry）错误发生在我的 while 循环中的 test.c 中，我在其中放置了 //ERROR。怎么了？

test.c

#include "mentry.h"
#include "mlist.h"

int main() {
  FILE *fPtr = fopen("S.txt", "r");
  MList *ml = ml_create();

  MEntry *m2;
  int i = 1;
  while ((m2 = me_get(fPtr)) != NULL) {
    unsigned long int hash = me_hash(m2, ml->numbuckets); // ERROR HERE
    i++;
  }

  return 0;
}

mlist.c

#include "mentry.h"
#include "mlist.h"

#define NUMBUCKETS 3
#define BUCKETSIZE 5

typedef struct bucket {
  int size; // number of elements in this bucket
  MEntry *entries; // array of MEntries
} Bucket;

typedef struct mlist {
  int numbuckets; // number of buckets
  Bucket **buckets; // an array of Bucket pointers
} MList;

/* ml_create  - creates a new mailing list
              - returns pointer to start of mailing list*/
MList *ml_create(void) {
  MList *ml = malloc(sizeof(MList));

  ml->numbuckets = NUMBUCKETS; // random initial number
                               // will increment once a bucket is full

  // init Buckets
  int b;
  for (b=0; b<ml->numbuckets; b++) {
    Bucket *bk = malloc(sizeof(Bucket));
    bk->size = 0;
    bk->entries = calloc(BUCKETSIZE, sizeof(MEntry));
    ml->buckets[b] = bk;
  }

  return ml;
}

mlist.h

#ifndef _MLIST_H_
#define _MLIST_H_

#include "mentry.h"

typedef struct mlist MList;

/* ml_create  - creates a new mailing list
              - returns pointer to start of mailing list*/
MList *ml_create(void);

#endif /* _MLIST_H_ */

Answer 1

What's wrong?

仅当 MList 的完整定义在该行可见时，您才可以使用 ml->numbuckets。

由于 MList 的完整定义仅在 mlist.c 中可见，您只能在该文件中访问 struct 的成员。

一种方法是在 mlist.h:

中声明一个函数

unsigned long int me_hash_list(MEntry* m1, MList* m2);

并在mlist.c中定义为：

unsigned long int me_hash_list(MEntry* m1, MList* m2)
{
   return me_hash(m1, m2->numbuckets);
}

然后从 main.

调用 me_hash_list

while ((m2 = me_get(fPtr)) != NULL) {
  unsigned long int hash = me_hash_list(m2, ml);
  i++;
}

Answer 2

当您尝试访问 main 中的 ml->numbuckets 时，它所知道的 m1 类型是这样的：

typedef struct mlist MList;

它知道 MList 是一种结构类型，但它对其中的内容一无所知。

你需要把完整的定义放在mlist.h:

#ifndef _MLIST_H_
#define _MLIST_H_

#include "mentry.h"

typedef struct mlist {
  int numbuckets; // number of buckets
  Bucket **buckets; // an array of Bucket pointers
} MList;

/* ml_create  - creates a new mailing list
              - returns pointer to start of mailing list*/
MList *ml_create(void);

#endif /* _MLIST_H_ */

"Dereferencing pointer to incomplete type"，typedef 没问题

"Dereferencing pointer to incomplete type", typedefs are ok

c

struct

types

dereference