struct x vs x_t in C

Question

In my recent operating systems class we have a bunch of objects defined as such:

typedef struct someobj {
  ... stuff ...
} someobj_t;

I know what that does just fine.

The question is that sometimes in the given support code the structs were refered to as struct someobj *some, and sometimes as someobj_t *some. Is there an actual / useful reason to refer to structs in these two different ways, or is just a stylistic difference?

Answer 1

While it's up to you whether you use a typedef or the struct name, there is a very good reason not to use typedef names ending in _t. All such names are reserved by POSIX for use by the implementation, and may refer to implementation-specific types or may be standardized in future versions of POSIX. Unfortunately many library authors ignore this.

Personally I prefer not to use typedef for structures, but if you do choose to use it, at least avoid the reserved namespace.

Answer 2

Assuming we're asking about the following code (there's no typedef in the question as I'm writing, but I'm assuming it was meant to be there):

typedef struct someobj {
    // content
} someobj_t;

Actually usually it'd be sufficient to omit the name someobj and use someobj_t consistently. However there's that situation when you want the struct to refer to itself:

typedef struct someobj {
    struct someobj* next;
    // cannot say someobj_t* yet - typedef not complete
} someobj_t;

// and from now on, both struct someobj and`someobj_t are equivalent