Why use "." in the struct in this way?

Why use "." in the struct in this way?

[lx]

hi all:
       why use the struct in this way by "."

for example, *.owner* instead of *owner* , why?
Thank you.

1203 <http://lxr.oss.org.cn/source/fs/ext2/super.c?v=2.6.16#L1203>
static struct file_system_type
<http://lxr.oss.org.cn/ident?v=2.6.16;i=file_system_type> ext2_fs_type
<http://lxr.oss.org.cn/ident?v=2.6.16;i=ext2_fs_type> = {1204
<http://lxr.oss.org.cn/source/fs/ext2/super.c?v=2.6.16#L1204>
.owner          = THIS_MODULE
<http://lxr.oss.org.cn/ident?v=2.6.16;i=THIS_MODULE>,1205
<http://lxr.oss.org.cn/source/fs/ext2/super.c?v=2.6.16#L1205>
.name <http://lxr.oss.org.cn/ident?v=2.6.16;i=name>           =
*"ext2"*,1206 <http://lxr.oss.org.cn/source/fs/ext2/super.c?v=2.6.16#L1206>
        .get_sb <http://lxr.oss.org.cn/ident?v=2.6.16;i=get_sb>
 = ext2_get_sb <http://lxr.oss.org.cn/ident?v=2.6.16;i=ext2_get_sb>,1207
<http://lxr.oss.org.cn/source/fs/ext2/super.c?v=2.6.16#L1207>
.kill_sb        = kill_block_super
<http://lxr.oss.org.cn/ident?v=2.6.16;i=kill_block_super>,1208
<http://lxr.oss.org.cn/source/fs/ext2/super.c?v=2.6.16#L1208>
.fs_flags       = FS_REQUIRES_DEV
<http://lxr.oss.org.cn/ident?v=2.6.16;i=FS_REQUIRES_DEV>,1209
<http://lxr.oss.org.cn/source/fs/ext2/super.c?v=2.6.16#L1209> };1210
<http://lxr.oss.org.cn/source/fs/ext2/super.c?v=2.6.16#L1210>
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Why use "." in the struct in this way?

[Prashant Shah]

Hi,

On Mon, Jul 29, 2013 at 8:26 PM, lx <lxlenovostar@gmail.com> wrote:
> hi all:
>        why use the struct in this way by "."
>

http://stackoverflow.com/questions/3016107/what-is-tagged-structure-initialization-syntax

The new specification of C language (C99) allows you to use "tagged"
initializers by supplying the desired member name within the {}

Why use "." in the struct in this way?

[Alexandru Juncu]

On 29 July 2013 17:56, lx <lxlenovostar@gmail.com> wrote:
> hi all:
>        why use the struct in this way by "."
>
> for example, .owner instead of owner , why?
> Thank you.
>
> 1203 static struct file_system_type ext2_fs_type = {
> 1204         .owner          = THIS_MODULE,
> 1205         .name           = "ext2",
> 1206         .get_sb         = ext2_get_sb,
> 1207         .kill_sb        = kill_block_super,
> 1208         .fs_flags       = FS_REQUIRES_DEV,
> 1209 };
> 1210


If you notice the definition of struct file_system_type [1], you will
see that the structure has more fields than you are initiating. In
this case, you just want to refer to some of the fields in the
structure.
You either give all fields a value (in order), or use the .field to
just refer to a single field and set a value for it.

[1] http://lxr.oss.org.cn/source/include/linux/fs.h?v=2.6.16#L1240

Why use "." in the struct in this way?

[Dave Hellewell]

On 30/07/13 00:56, lx wrote:
> hi all:
>        why use the struct in this way by "."
> 
> for example, *.owner* instead of *owner* , why? 

It's utilising a feature known as designated initialisers. Essentially,
using this technique, struct members may be initialised out of order
from the way the struct is defined.

cf.
http://en.wikipedia.org/wiki/Struct_(C_programming_language)#Struct_initialization

Cheers,

Dave