循环结构声明C.

Question

I have to declare a structure that depends on another structure declaration, but gcc keeps complaining and I've reached a point where I can't work around it by simply moving the code around. Here's the deal:

typedef struct inodes
{
    unsigned short int  numInode;
    ListaBlocos         *blocos;
    ListaInodes         *filhos;
    Meta                metaDados;
    unsigned short int  tempo;
} Inode;


typedef struct listablocos
{
    Bloco               bloco;
    struct listablocos  *prox;
} ListaBlocos;

typedef struct listainodes
{
    Inode               inode;
    struct listainodes  *prox;
} ListaInodes;

Basically, ListaInodes is a list that has instances of the Inode type in it. So I'd have to declare Inode before it. But if I do, gcc will complain with this:

error: unknown type name 'ListaInodes'

because one of the fields of Inode is a list of other Inodes. How can this be fixed, preferrably with not too drastic changes to the code?

Answer 1

Just add the typedef before the definition.

typedef struct listainodes ListaInodes;
typedef struct inodes Inode;
typedef struct listablocos ListaBlocos;

struct inodes
{
    unsigned short int  numInode;
    ListaBlocos         *blocos;
    ListaInodes         *filhos;
    Meta                metaDados;
    unsigned short int  tempo;
};

struct listablocos
{
    Bloco         bloco;
    ListaBlocos  *prox;
};

struct listainodes
{
    Inode        inode;
    ListaInodes *prox;
};

As you can see you can even define the struct s in the implementation file instead of the header, thus hiding the structure definition from the potential structure users, adding accessor get/set like functions, you can add functionality while the struct is effectively hidden, a very common technique with numerous benefits, like avoiding the misuse of a given struct field.