如何在C中获取结构字段

Question

I have the code:

main() 
{
   typedef struct
   {
      int data;
   } Information;

   typedef Information *PtrInformation;

   typedef struct InformationListStruct *PtrInformationListStruct;

   typedef struct InformationListStruct
   {
      PtrInformationListStruct ptrNext;
      PtrInformation ptrInf;
   } PtrInformationListStructElement;

   //==============================

   PtrInformationListStruct list;
   list = (PtrInformationListStruct)malloc(sizeof(InformationListStruct));
   PtrInformation ptr = (*list).ptrInf;  // error !!!

}

The compiler throw the error:

• "ptrInf" is not a member of InformationListStruct, because the type is not yet defined in function main()

If I put this line:

typedef struct InformationListStruct *PtrInformationListStruct;

after this lines:

   typedef struct InformationListStruct
   {
      PtrInformationListStruct ptrNext;
      PtrInformation ptrInf;
   } PtrInformationListStructElement;

then other error appears:

• Type name expected in function main()
• Declaration missing ; in function main()

How to get "ptrInf" correctly?

Answer 1

您不应该在C中malloc()的返回值。此外，请使用sizeof ，不要重复类型名称：

list = malloc(sizeof *list);

Answer 2

You need

 list = (PtrInformationListStruct)malloc(sizeof(struct InformationListStruct));
 //                                               |
 //                                          note struct keyword

or

 list = (PtrInformationListStruct)malloc(sizeof(PtrInformationListStructElement));

since you have a typedef for it.

Answer 3

Which Compiler are you using, in visual studio , your code is compiling successfully. Please avoid type definations inside the body of a function.