C - Forward declaration for struct and function

Question

I'm trying to figure out how exactly forward declarations interact. When forward declaring a function that takes a typedef'd struct, is there a way to just get the compiler to accept a previously forward declared (but not actually defined) struct as a parameter?

The code that I've got working:

typedef struct{
  int year;
  char make[STR_SIZE];
  char model[STR_SIZE];
  char color[STR_SIZE];
  float engineSize;
}automobileType;

void printCarDeets(automobileType *);

What I wish I could do:

struct automobileType;
void printCarDeets(automobileType *);

//Defining both the struct (with typedef) and the function later

I feel like I'm either missing something really basic or not understanding how the compiler deals with forward declarations of structs.

Answer 1

Typedefs and struct names are in different namespaces. So struct automobileType and automobileType are not the same thing.

You need to give your anonymous struct a tag name in order to do this.

The definition in your .c file:

typedef struct automobileType{
  int year;
  char make[STR_SIZE];
  char model[STR_SIZE];
  char color[STR_SIZE];
  float engineSize;
}automobileType;

The declaration in your header file:

typedef struct automobileType automobileType;
void printCarDeets(automobileType *);