invalid application of 'sizeof' to incomplete type list struct C

问题:

I'm trying to implement an replacement algorithm that deals with page faults. So i'm trying to creat a circular linked list using malloc and im getting the following error: "invalid application of sizeof' to incomplete typepageInMemory'.following is the code:

 typedef  struct {              int use;              int reference;             int free;             struct pageInMemory* next;             } pageInMemory;               int main()             {                  int i;                 struct pageInMemory* start, *nn, *temp, *hand;                 start = NULL;                      for(i=0; i< pNum; i++)                      {                 nn = (struct pageInMemory *)malloc(sizeof(struct pageInMemory));                         nn->use = 0;                         nn->free = 1;                          if(start==NULL)                         {                             nn->next = nn;                             start =nn;                         }                          else                         {     // sfhsdifhsdifj sdijfjsd                              temp = start;                             while(temp->next != start)                             {                                 temp = temp->next;                              }                              temp->next = nn;                             nn->next = start;                             start = nn;                          }                         }                    hand = start;                 temp = start;               while(temp->next != start->next)              {                 printf("%d\n", temp->use); //hi              }                    return 0;// bye              }   

so am i not supposed to use malloc this way ?

回答1:

change your struct definition as

struct pageInMemory{              int use;             int reference;             int free;             struct pageInMemory* next;             }; 

to get your code working. And just for your info do not typecast void* coming from malloc.

回答2:

pageInMemory is itself defined as type. So instead of this,

nn = (struct pageInMemory *)malloc(sizeof(struct pageInMemory)) 

Use this,

nn = (pageInMemory *)malloc(sizeof(pageInMemory)) 

回答3:

It should be either:

typedef  struct pageInMemory_s {          int use;          int reference;         int free;         struct pageInMemory_s * next;         } pageInMemory;  pageInMemory* start, *nn, *temp, *hand; ...  nn = malloc(sizeof(pageInMemory)); 

or

struct pageInMemory {          int use;          int reference;         int free;         struct pageInMemory* next;         };  struct pageInMemory* start, *nn, *temp, *hand; ...  nn = malloc(sizeof(struct pageInMemory)); 

A third variant would be:

typedef  struct pageInMemory {          int use;          int reference;         int free;         struct pageInMemory * next;         } pageInMemory;  pageInMemory* start, *nn, *temp, *hand; ...  

For this 3rd option you can use:

nn = malloc(sizeof(pageInMemory)); 

or

nn = malloc(sizeof(struct pageInMemory)); 

This latter variation I feel is very irritating as there is one name for two different things:

• The structure definition/declaration struct pageInMemory
• The type definition/declaration pageInMemory

I would not recommend to use this 3rd option, but the second.

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