[Asterisk-Users] OT - C structure question

[Race Vanderdecken]

Greetings,

First, you are hereby admonished for asking programming/development
questions on the user list. 

C does not have a way to do this directly. Yes, you could use some
preprocessing macro but the code would be a nightmare.

You actually gave yourself the answer in your questions.

You can use a "map" data structure to do this.

GetChannelData( char* Variable )
{
	return( mapX[variable] );
}

A "map" is a two dimensional array where the first column holds a
character string and the second column holds the data associated with
the array.

http://www.sgi.com/tech/stl/Map.html -- SGI gives a good reference and
some great tutorial like information on advanced data structures.

A less intense tutorial is here
http://www.cprogramming.com/tutorial/stl/stlmap.html

The STL, standard template library, is a C/C++ library that allows you
to create a map for your particular code.

You enter each "variable" and its associated value into the map. 
Then you call y = mapX[ variable ] and it gives you back the value you
assigned to it.

mapX[] is not really an array, so you can do mapx[1] because there is
not really a mapX[1] value since all the indexing is done privately you
don't really know the real location of where your "variable" value went
in the array. 

For ( y = variable[x]; x < 10; x++ )
{
	mapX[ y ] = x;
}

While this may look like an array of 10 items it is not, the "[]"
brackets are overloaded to make retrieving stuff eaiser.

Race "The Tyrant" Vanderdecken

An next time you have a code question be sure to use asterisk-dev list
or others my flame you.


-----Original Message-----
From: asterisk-users-bounces at lists.digium.com
[mailto:asterisk-users-bounces at lists.digium.com] On Behalf Of Asterisk
Sent: Thursday, February 24, 2005 11:42 AM
To: asterisk-users at lists.digium.com
Subject: [Asterisk-Users] OT - C structure question

I hae tried searching the web for the answer, but, man is there a lot of

    pages ... :(

in the language I develop in, if I have a structure I can dynamically 
refer to the contents of a field of the structure like so:

MESSAGE SomeStructure:Field(SomeFieldName):Value

where SomeFieldName is either a quoted constant or a variable
expressions

In "C", I beleive that you can refer to the contents of a "field" in a 
"structure" like so:

chan->context or
chan->exten

Is is possible to refer to these fields like

chan->(variable) where variable is either "context" or "exten" or an 
expression that resolves to a valid fieldname of the structure ?

My reason for asking is that I want to create an application that would 
take a channel and a field name and return the value of the field.

for example

GetChannelData("context")
GetChannelData("exten")

and I didn't want to have to declare a massive case statement, and have 
to modify the app everytime some new fields were added to the structure.

I know that some of these variables are already exposed, but was wanting

to get some other values.

Julian


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