indirection

#indirection

##Syntax targetType @ ( expn )

##Description The indirection operator @ is used to access values that lie at absolute machine addresses in the computer's memory. This is dangerous and implementation-dependent and can cause arbitrary corruption of data and programs.

##Example Copy the byte value at memory location 246 into b and then set that memory byte to zero.

    var b : nat1            % One byte natural number
    b := nat1 @ (246)
    nat1 @ (246) := 0

##Details The form of targetType must be one of:

In form (a) the beginning identifier id must be the name of a module, monitor or class that exports the typeId. Each of numberOfCharacters and maximumLength must be compile time integer expressions. These are the same target types as in type cheats.

The indirection operator @ takes an integer as an address. This value must fit in the range of addressint. See addressint. See also pointer types and the ^ operator (which accesses objects located by pointers).

    (a) [ id . ] typeId
    (b) int, int1, int2 or int4
    (c) nat, nat1, nat2 or nat4
    (d) boolean
    (e) char [ ( numberOfCharacters ) ]
    (f) string [ ( maximumLength ) ]
    (g) addressint

##See also cheat.html. See also explicitintegerconstant.html (which explains how to write hexadecimal constants, which are often used for addresses).