CODEWITHSUNDEEP
cstructpointers
claf
claf

Reputation: 9263

C: pointer to struct in the struct definition

How can I have a pointer to the next struct in the definition of this struct:

typedef struct A {
  int a;
  int b;
  A*  next;
} A;

this is how I first wrote it but it does not work.

Upvotes: 61

Views: 92327

Answers (6)

CB Bailey
CB Bailey

Reputation: 793179

You can define the typedef and forward declare the struct first in one statement, and then define the struct in a subsequent definition.

typedef struct A A;

struct A
{
    int a;
    int b;
    A* next;
};

Edit: As others have mentioned, without the forward declaration the struct name is still valid inside the struct definition (i.e. you can used struct A), but the typedef is not available until after the typedef definition is complete (so using just A wouldn't be valid). This may not matter too much with just one pointer member, but if you have a complex data structure with lots of self-type pointers, may be less wieldy.

Upvotes: 87

user7296055
user7296055

Reputation: 105

typedef struct {
 values
} NAME;

This is shorter way to typedef a struct i think its the easiest notation, just don't put the name infront but behind.

you can then call it like 

NAME n;  

NAME *n; // if you'd like a ptr to it.

Anything wrong with this approach?

Upvotes: 0

ephemient
ephemient

Reputation: 205014

Please, you're in C, not C++.

If you really must typedef a struct (and most programmers that I work with would not¹), do this:

typedef struct _A {
    int a;
    int b;
    struct _A *next;
} A;

to clearly differentiate between _A (in the struct namespace) and A (in the type namespace).

¹typedef hides the size and storage of the type it points to ― the argument (and I agree) is that in a low-level language like C, trying to hide anything is harmful and counterproductive. Get used to typing struct A whenever you mean struct A.

Upvotes: 9

Miles D
Miles D

Reputation: 8060

You are missing the struct before the A*

  typedef struct A {
    int a;
    int b;
    struct A* next;
  } A;

Upvotes: 21

qrdl
qrdl

Reputation: 35008

You can go without forward declaration:

struct A {
    int a;
    int b;
    struct A *next;
};

Upvotes: 14

Chris Young
Chris Young

Reputation: 15767

In addition to the first answer, without a typedef and forward declaration, this should be fine too.

struct A 
{ 
    int a; 
    int b; 
    struct A *next; 
};

Upvotes: 68

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