c - "Dereferencing pointer to incomplete type", typedefs 没问题

Question

我正在尝试实现一个哈希表。我收到上述错误，但 AFAIK 我已经正确声明了我所有的结构/typedef。 (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？

测试.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

当您尝试访问 main 中的 ml->numbuckets 时，它所知道的关于 m1 类型的所有信息是:

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中:

#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_ */