Unusual C construct - What is it?

[Ramon F Herrera]

I was looking at some open source code, and found something that I had
never seen before:

const struct ast_datastore_i nfo dialed_interfac e_info = {
.type ="dialed-interface",
.destroy = dialed_interfac e_destroy,
.duplicate = dialed_interfac e_duplicate,
};
What the heck are those dotted variables (?) fields(?). I don't recall
seeing that in the K&R.

I include the full file below.

-Ramon

---------------
/*
* Asterisk -- An open source telephony toolkit.
*
* Copyright (C) 1999 - 2007, Digium, Inc.
*
* Mark Michelson <mm********@dig ium.com>
*
* See http://www.asterisk.org for more information about
* the Asterisk project. Please do not directly contact
* any of the maintainers of this project for assistance;
* the project provides a web site, mailing lists and IRC
* channels for your use.
*
* This program is free software, distributed under the terms of
* the GNU General Public License Version 2. See the LICENSE file
* at the top of the source tree.
*/

/*! \file
*
* \brief globally-accessible datastore information and callbacks
*
* \author Mark Michelson <mm********@dig ium.com>
*/

#include "asterisk/global_datastor es.h"
#include "asterisk/linkedlists.h"

static void dialed_interfac e_destroy(void *data)
{
struct ast_dialed_inte rface *di = NULL;
AST_LIST_HEAD(, ast_dialed_inte rface) *dialed_interfa ce_list = data;

if (!dialed_interf ace_list)
return;

AST_LIST_LOCK(d ialed_interface _list);
while ((di = AST_LIST_REMOVE _HEAD(dialed_in terface_list, list)))
ast_free(di);
AST_LIST_UNLOCK (dialed_interfa ce_list);

AST_LIST_HEAD_D ESTROY(dialed_i nterface_list);
ast_free(dialed _interface_list );
}

static void *dialed_interfa ce_duplicate(vo id *data)
{
struct ast_dialed_inte rface *di = NULL;
AST_LIST_HEAD(, ast_dialed_inte rface) *old_list;
AST_LIST_HEAD(, ast_dialed_inte rface) *new_list = NULL;

if(!(old_list = data))
return NULL;

if(!(new_list = ast_calloc(1, sizeof(*new_lis t))))
return NULL;

AST_LIST_HEAD_I NIT(new_list);
AST_LIST_LOCK(o ld_list);
AST_LIST_TRAVER SE(old_list, di, list) {
struct ast_dialed_inte rface *di2 = ast_calloc(1, sizeof(*di2) +
strlen(di->interface));
if(!di2) {
AST_LIST_UNLOCK (old_list);
dialed_interfac e_destroy(new_l ist);
return NULL;
}
strcpy(di2->interface, di->interface);
AST_LIST_INSERT _TAIL(new_list, di2, list);
}
AST_LIST_UNLOCK (old_list);

return new_list;
}

const struct ast_datastore_i nfo dialed_interfac e_info = {
.type ="dialed-interface",
.destroy = dialed_interfac e_destroy,
.duplicate = dialed_interfac e_duplicate,
};

[Ian Collins]

Ramon F Herrera wrote:

[you posted to the wrong group]

I was looking at some open source code, and found something that I had
never seen before:

const struct ast_datastore_i nfo dialed_interfac e_info = {
.type ="dialed-interface",
.destroy = dialed_interfac e_destroy,
.duplicate = dialed_interfac e_duplicate,
};
What the heck are those dotted variables (?) fields(?). I don't recall
seeing that in the K&R.

You won't. Its C99 syntax.

--
Ian Collins.

[Abhishek Padmanabh]

On Dec 24, 11:07*am, Ramon F Herrera <ra...@conexus. netwrote:

I was looking at some open source code, and found something that I had
never seen before:

const struct ast_datastore_i nfo dialed_interfac e_info = {
* * * * .type ="dialed-interface",
* * * * .destroy = dialed_interfac e_destroy,
* * * * .duplicate = dialed_interfac e_duplicate,

};

What the heck are those dotted variables (?) fields(?). I don't recall
seeing that in the K&R.

This is part of C99 syntax and those variables are designated
initialisers. It makes it easier to track which fields are set during
that initialization. It is not valid in C++ though.

[mczard]

const struct ast_datastore_i nfo dialed_interfac e_info = {

* * * * .type ="dialed-interface",
* * * * .destroy = dialed_interfac e_destroy,
* * * * .duplicate = dialed_interfac e_duplicate,

This is part of C99 syntax and those variables are designated
initialisers. It makes it easier to track which fields are set during
that initialization. It is not valid in C++ though.

If you need such a thing in C++, you have to use external
configuration files (try http://harpoon.sourceforge.net; my project to
be honest). I really wish it were a part of C++, as well as list
literals; and not only for initialization. For example:

draw_line( Point( x = 10, y = 25 ), Point( x = 50, y = 25 ) );

std::vector<int list( { 1, 4, 5, 2 } );

[=?UTF-8?B?RXJpayBXaWtzdHLDtm0=?=]

On 2007-12-25 18:47, mc****@poczta.o net.pl wrote:

const struct ast_datastore_i nfo dialed_interfac e_info = {
.type ="dialed-interface",
.destroy = dialed_interfac e_destroy,
.duplicate = dialed_interfac e_duplicate,

This is part of C99 syntax and those variables are designated
initialisers . It makes it easier to track which fields are set during
that initialization. It is not valid in C++ though.

If you need such a thing in C++, you have to use external
configuration files (try http://harpoon.sourceforge.net; my project to
be honest). I really wish it were a part of C++, as well as list
literals; and not only for initialization. For example:

The fact that C++ have constructors mitigates the problem slightly, and
if that is not enough you can use comments.

struct Point {
Point(intx, int y);
};

Point(/*x = */ 10, /*y = */ 25);

draw_line( Point( x = 10, y = 25 ), Point( x = 50, y = 25 ) );

std::vector<int list( { 1, 4, 5, 2 } );

Will be in the next version of the standard, but with slightly different
syntax.

--
Erik Wikström

[LR]

Erik Wikström wrote:

On 2007-12-25 18:47, mc****@poczta.o net.pl wrote:

>>>const struct ast_datastore_i nfo dialed_interfac e_info = {
.type ="dialed-interface",
.destroy = dialed_interfac e_destroy,
.duplicate = dialed_interfac e_duplicate,
This is part of C99 syntax and those variables are designated
initialiser s. It makes it easier to track which fields are set during
that initialization. It is not valid in C++ though.

If you need such a thing in C++, you have to use external
configuratio n files (try http://harpoon.sourceforge.net; my project to
be honest). I really wish it were a part of C++, as well as list
literals; and not only for initialization. For example:

The fact that C++ have constructors mitigates the problem slightly, and
if that is not enough you can use comments.

struct Point {
Point(intx, int y);
};

Point(/*x = */ 10, /*y = */ 25);

>draw_line( Point( x = 10, y = 25 ), Point( x = 50, y = 25 ) );

The named parameter idiom might be useful,
http://www.parashift.com/c++-faq-lit...html#faq-10.18

LR