"Strange" data type

alaios · 04-30-2012, 10:47 AM

Dear all I have found in a c library the following data type

for the IPv6 loopback device:

Code:

#define IN6ADDR_LOOPBACK_INIT { { { 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1 } } }

Could you please help me understand it?

I would like to thank you in advance for your help

B.R
Alex

Snark1994 · 04-30-2012, 10:51 AM

Well... That's just a define statement, so it's essentially a find-and-replace. My guess is you're going to be running something like:

Code:

//5s are arbitrary - but 'IN6ADDR_LOOPBACK_INIT' is an 
//array of an array of an array
char something[5][5][16] = IN6ADDR_LOOPBACK_INIT;

to initialise your list of whatevers to the value you typed in.

As you can tell, I'm not exactly familiar with IPv6 C code, just with the general structure of what you'd be doing

alaios · 05-01-2012, 06:08 AM

I know this is a define statement (find and replace...) . I found it in one in a library file .h

what I do not understand are the {} brackets part...

Could you please help me understand that?

millgates · 05-02-2012, 02:45 AM

The braces are used to initialize arrays. Example

Code:

int array[] = {1, 2, 3, 5, 7};

If you have a 2D array, it may look like this:

Code:

int a[][2] = { {1,2}, {1,3}, {1,4} };

The array elements are in braces, and each element itself is also an array. So what you have in your first post is an initialization of a 3D array.

Snark1994 · 05-02-2012, 01:20 PM

millgates is correct.

I just googled for IN6ADDR_LOOPBACK_INIT and found this, which is a more in-depth discussion pf the exact piece of code you're looking at, with some code examples. There are several discussions there which you can look up

Hope this helps,