C structs don't define types?

Question

I\'ve just started learning C with a professional Java background and some (if no too much) C++ knowledge, and I was astonished that this doesn\'t work in C:

str         


        

Answer 1

You first need to make Point a type like :

typedef struct Point {
    int x;
    int y;
} Point;

This allows you to use Point as a type, or struct Point

I.e:

Point *p;

sizeof(struct Point);

Some people prefer to make the name of the structure different from the type being created, such as:

typedef struct _point {
       ...
} Point;

You'll run into both. The last example tells me that I should not use struct _point, its not meant to be exposed except as the type Point.

Answer 2

No, a struct do not define a new type. What you need is:

typedef struct {
   int x; int y;
} Point;

Now Point is new type you can use:

Point p;
p.x = 0; p.y = 0;

Answer 3

struct Point is the type just like union Foo would be a type. You can use typedef to alias it to another name - typedef struct Point Point;.

Answer 4

Structs are not types. You can create a point from a struct as follows:

struct Point p;
p.x = 0;
p.y = 0;

If you want to use a struct as a type, you have to typedef it. This works in both C and C++:

typedef struct _point {
    int x;
    int y;
} Point;

Always give your struct a name though, if you have to forward declare it to be able to have pointers to a struct of the same type or circular dependencies.