C Structs and Typedef

Help me understand structs and typedef.

What is the difference between:
struct tag_name{ type member; }
typedef struct tag_name{ type member; } struct_alias;

Why is the tag_name optional in number 2 if there is no self-referential pointer?

When creating an instance of a struct, when do you have to use:
tag_name instance;
and when:
struct tag_name instance;
?

Is using:
typedef struct tag{} alias
making it possible to say:
alias instance;
instead of:
struct tag instance;
?

Also when is the tag needed there?
How do you create an instance of:
typedef struct {} alias

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Use C++ and classes instead.

Using C++ won't help me understand C any better.

>>4
You haven't tried

sir lelington

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Just fucking read K&R2 and stop asking stupid quesitons.

Most of your questions are answered by these few points:

1. Unsure? Try compiling it, changing it, compiling it again.
2. "typedef" makes an alias of another type. e.g. "typedef int** ppint;" would make a "ppint" type exactly equivalent to "int**". It follows a similar syntax to variable declarations except it declares a type instead of a variable.
3. You can give typedef structs an empty tag for the same reason you can give struct variables an empty tag, e.g.
struct {
  int x, y;
} shit;
The reason is that you can refer to the typedef or variable by its actual name.
4. In the self-referential pointer case you should be asking why it's not possible to use the typedef - and the answer is because the typedef is evaluated only after the struct has been parsed.

Dubs.

>>11
Well fuck me! My system clock is a few seconds ahead it seems. I'm sorry guys, I really dropped the ball on this one.

>>9
>le pedophile sage

>>11
check ''em

install gentoo

>>1
In addition to what >>10-san said, for historical reasons struct tags live in a different namespace in C -- if you have a struct type named "s", you have to always refer to it as "struct s". Which, together with a separate namespace for values, allows http://ideone.com/JQJ0nd

>le pedophile san

So how many different identificator/tag namespaces does C have in all, five?

- variable tags
- type tags
- struct tags
- struct field tags
- label tags (for the goto shit)

Did I miss anything?

>>18
It turned out that I lied about the separate namespace for values, it after a bork bork; declaration bork begins to refer to the variable.

Anyway,

6.2.3 Name spaces of identifiers

If more than one declaration of a particular identifier is visible at any point in a translation unit, the syntactic context disambiguates uses that refer to different entities. Thus, there are separate name spaces for various categories of identifiers, as follows:
— label names (disambiguated by the syntax of the label declaration and use);
— the tags of structures, unions, and enumerations (disambiguated by following any) of the keywords struct, union, or enum);
— the members of structures or unions; each structure or union has a separate name space for its members (disambiguated by the type of the expression used to access the member via the . or -> operator);
— all other identifiers, called ordinary identifiers (declared in ordinary declarators or as
enumeration constants).

*YOU HAVE BEEN VISITED BY LE TOP LEL OF COMEDY GOLD** POST THIS IN 3 threads or lose your sides!
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>>18
identificator
Russiafag detected.

dubs