GENERAL: FORWARD STRUCTURE REFERENCES IN C

Information in this article applies to:

• C166 Version 3.12
• C166 Version 4.05
• C251 Version 1.24
• C251 Version 2.14
• C51 Version 5.50a
• C51 Version 6.01

QUESTION

How can I create several structures that reference each other. It appears that there is a problem with C understanding forward recerences to structures. For example, the following code:

struct a
  {
  struct b *pb;
  };

struct b
  {
  struct a *pa;
  };


struct a a1 = { &b1 };
struct b b1 = { &a1 };

Generates the following error:

*** ERROR C202 IN LINE 12 OF .\JJ.C: 'b1': undefined identifier

How do I do this in C?

ANSWER

Change your code to the following to use forward struct references.

struct a
  {
  struct b *pb;
  };

struct b
  {
  struct a *pa;
  };

struct b b1;   /* declare the b1 but don't define it -- this makes it work */
struct a a1 = { &b1 };
struct b b1 = { &a1 };

Last Reviewed: Thursday, April 27, 2000