Address of a variable: Difference between revisions

=={{header|ALGOL 68}}==

Basically ALGOL 68 refuses to let the programmer access the memory directly. The language does

allow "references" any variables. These references are effectively the address a particular

variable. But the value of the actual address is not available for printing or any arithmetic.

<pre>

[4]INT test := (222,444,666,888);

REF INT reference := test[3];

REF INT(reference) := reference + 111;

print(("test value is now: ",test))

</pre>

Output:

<pre>

test value is now: +222 +444 +777 +888

</pre>

The other reason specific addresses are using in languages like [[C]] to manipulate

devices. For this purpose site are expected to implement channels for their programmers to use.

To quote the ALGOL 68 Revised Report: <i>A "channel" corresponds to one or more physical devices (e.g.,

a card reader, a card punch or a line printer, or even to a set up in

nuclear physics the results of which are collected by the computer),

or to a filestore maintained by the operating system.</i>

To establish a channel with such a device there is a special standard procedure:<pre>

PROC establish = (REF FILE file, STRING idf, CHANNEL chan, INT p, l, c) INT: ~ </pre>

Where the <code>idf</code> string is text describing which device to open, and possibly options.

And <code>chan</code> is the actual device type. Standard CHANNEL in ALGOL 68 are <code>stand in chan</code>,

<code>stand out chan</code>, and <code>stand back chan</code>. Site would be expected to implement their own

CHANNELS for database queries and particle accelerators etc.