Re: Accessing elements of static array by name

From:

=?UTF-8?B?RXJpayBXaWtzdHLDtm0=?= <Erik-wikstrom@telia.com>

Newsgroups:

comp.lang.c++

Date:

Sun, 26 Aug 2007 17:27:20 GMT

Message-ID:

<YJiAi.7002$ZA.3732@newsb.telia.net>

On 2007-08-26 19:10, Paul Brettschneider wrote:

On Sun, 26 Aug 2007 11:03:36 +0000, Erik Wikstr??m wrote:

On 2007-08-26 11:20, Paul Brettschneider wrote:

Hello,

I have a global static array of structs and want to access a given
element using an identifier. I don't want to use the element subscript,
because it will change if I insert elements before the element I
want to access. In assembler I would simply add a label in front
of the element, but this doesn't work in C++.

[...]

Is there a way to do this in C++ (maybe some preprocessor tricks)?

There are probably some pre-processor trick you can use, but I suspect
that would be the wrong solution. Since you mentioned assembly I suspect
you have a background with that and might thus not be very familiar with
the C++ way of doing things. If you could explain a little bit about
what you are trying to solve I might be able to give you better advice.

I have, for example, a number of "Server-Objects" which are registered
when connecting to the server and can be used afterwards. When registering
or when generating statistics, it is convenient to loop over an array,
later I want to access them by name.

What I do right now is define global objects and then construct an array
of pointers:

static A element_a = { "a" };
static A element_b = { "b" };
static A element_c = { "c" };

static A *array[] = {
        &element_a,
        &element_b,
        &element_c,
        // ...
        NULL // sentinel
};

You could use std::map<std::string, A> servers. Then you could access a
specific one using servers["the_one"], and you can also loop over all of
them using iterators.

Another possibility is to do it the other way round, like Gianni suggested:
have an array of objects and initialise references with a find()-function
at program-initialisation time.

I was hoping for a more convenient way.

BTW: I think accessing array-elements by name would sometimes be
convenient for local arrays too:

int func()
{
int array[] = {1, element2: 2, 3 };
return element2; // Alias for array[1]
}

If it's only for a few elements a reference will do, if it's for many
elements perhaps they should not be in an array.

--
Erik Wikstr??m