Why use typedef on struct and union?

Question

I was wondering why you would use the specifier typedef on the types struct and union, because aren't they somewhat used to define your own type anyways?

Thanks!

@user2357112, sure? I mean, I have seen it been used in C++? — , May 05 '17 at 23:29
@Skizz - I would expect a user with high rep to know tags are for specifying the field of the question, and not for making your own answer correct — StoryTeller - Unslander Monica, May 05 '17 at 23:35
Probably because older c++ programmers all started with C, and got in the habit of doing this, even though it is not needed in c++. — Kenny Ostrom, May 05 '17 at 23:35
@StoryTeller, here is one the places I saw it: http://stackoverflow.com/a/1951401/7926026 — , May 05 '17 at 23:36
There is no reason ever to use `typedef` when defining a `struct` or `union`. There. I said it. — Galik, May 05 '17 at 23:36
Yeah, I'd definately put myself in the ;'older' category :-) — Skizz, May 05 '17 at 23:36
`C` programmers do it so they don't need to type `struct` everywhere. `C++` doesn't have that issue. — Galik, May 05 '17 at 23:37
@Hei - The question you linked is doubly tagged with C and C++. The answer is pure C. C++ programmers don't do it, not unless writing C bindings to their C++ library, any way. — StoryTeller - Unslander Monica, May 05 '17 at 23:37
Thanks guys! Let me try to read everything here and I will leave a comment :) — , May 05 '17 at 23:39

Skizz · Answer 1 · 2017-05-05T23:45:14.667

2

Edit Reading the standard the 'typedef' isn't required in C++ and is probably there for backward compatibility. Also, with 'typedef' the code would compile in both C and C++ compilers without change or '#if define' around it so it's probably a legacy code support thing.

I think people do it to save on typing! We're a lazy lot afterall. So instead of:-

struct SomeStruct
{
  // some data
};

struct SomeStruct first_instance;
struct SomeStruct second_instance;

you'd have this instead:-

typedef struct typedefSomeStruct
{
  // some data
} SomeStruct;

SomeStruct first_instance;
SomeStruct second_instance;

So when you declare instances of the type you don't need to prefix the 'struct' keyword.

edited May 05 '17 at 23:45

answered May 05 '17 at 23:31

Skizz

69,698
10
71
108

1

This is really a holdover from C, as C++ doesn't require the `struct` keyword when declaring them. – Phil M May 05 '17 at 23:32
4

This is tagged C++, you don't need to prefix it either way – StoryTeller - Unslander Monica May 05 '17 at 23:32
This answer doesn't work for `C++`. – Galik May 05 '17 at 23:39

Why use typedef on struct and union?

1 Answers1