Why are structures typedef'ed to their own names?

Question

In many places in code I have seen code like this:

typedef struct Name_of_Struct{
    //Things that the struct holds
} Name_of_Struct;

I don't seem to understand why such a declaration? Why is a struct typedef'ed to its own name? Isn't it like saying typedef Name_of_struct Name_of_Struct; ? I know there must be some reason behind such a declaration, as such instances of code are seen in good and highly used code bases like SDL.

Note that SDL is a C library that can be used from C++ as well. — Csq, Sep 28 '14 at 14:33
First and foremost, this is a C-specific declaration pattern. C, not C++. You tagged your question as [C++]. So, did you see it in C++ code (which is possible in shared C/C++ code)? Or did you simply mistag your question? — AnT stands with Russia, Sep 28 '14 at 14:36

score 4 · Accepted Answer · answered Sep 28 '14 at 14:25

In C++ you don't have to do that

However in C this is done in order to save some typing

struct Name_of_Struct{
    //Things that the struct holds
} ;

struct Name_of_Struct ss; // If not typedef'ed you'll have to use `struct`

But with typedef

typedef struct Name_of_Struct{
    //Things that the struct holds
} Name_of_Struct;

Name_of_Struct ss ; // Simply just use name of struct, avoid struct everywhere

score 1 · Answer 2 · answered Sep 28 '14 at 14:25

1

The code is probably shared between C and C++. The C Programming Language does not automatically create type names for user-created types (e.g., enum, struct, union). I haven't written a lot of C in recent years so this may have been changed in C99.

answered Sep 28 '14 at 14:25

D.Shawley

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Just curious as to where the initial down vote came from? – D.Shawley Sep 28 '14 at 14:27

Galik · Answer 3 · 2014-09-28T14:33:13.490

Specifying the name twice is redundant.

Originally in C the typedef was used so you didn't need to qualify the name with struct all the time. In C++ you can simply name the struct.

// C method

struct MyStruct {};

// need to qualify that name with `struct`

struct MyStruct s;

// C method avoiding typing `struct` all the time

typedef struct {} MyStruct;

MyStruct s; // no need to use `struct`

// C++ way

struct MyStruct {};

MyStruct s;

It seems some programmers have made a Frankenstein of the two methods.

Why are structures typedef'ed to their own names?

3 Answers3