C 链表结构中的未知类型名称

Question

I got a structure like this in a header file:

typedef struct {
    LIGNE *precedent;
    PERSONNE individu;
    LIGNE *suivant;
} LIGNE;

But when I compile, I got this error:

error: unknown type name ‘LIGNE’
  LIGNE *precedent;
  ^~~~~
error: unknown type name ‘LIGNE’
  LIGNE *suivant;

I don't understand where is the problem.

Answer 1

Put yourself in compilers shoes:

1: typedef struct {
2:     LIGNE *precedent;
3:     PERSONNE individu;
4:     LIGNE *suivant;
5: } LIGNE;

In line 2 you say that you want a pointer to something of type LIGNE . That's a problem for compiler since it has no idea what LIGNE is until line 5. Granted, this is compiler being a little dumb. A pointer to anything is the same size, so as far as layout of structure goes, it shouldn't matter. However, C compiler wants to know what sort of pointer this. As @Gerhardh suggested, you can trick it by prefixing lines 2 and 4 with struct . Compiler sees this and reads it as pointer to structure , suddenly no longer caring that it knows not anything about it.

Answer 2

This will work

typedef struct {
    struct LIGNE *precedent;
    PERSONNE individu;
    struct LIGNE *suivant;
} LIGNE;

Answer 3

As said in the commants and in the Tomo Ceferin 's answer, your compiler has no idea of what LIGNE is until line 5.

One solution would be to typedef your structure before its declaration:

typedef struct S_LIGNE LIGNE;

struct S_LIGNE {
    LIGNE *precedent;
    PERSONNE individu;
    LIGNE *suivant;
};

This way, your compiler knoww that LIGNE is a typedef for struct S_LIGNE .