| addressint | type |
| Syntax | addressint
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| Description | The addressint (address integer) type is an integer type whose range of value is the same as that of the underlying computer. This range is, by its nature, implementation-dependent. On 32-bit architectures, it is commonly the same range as nat4 (4-byte natural number).
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| Example | Record r contains three fields, one of which has type char(28). Variable a is an integer whose range of values is the same as the addresses of the underlying computer. This assigns B to the seventh character of a record of type r which is assumed to be located at absolute address a.
type r :
record
i : int
c28 : char (28)
c11 : char (11)
end record
var a : addressint % An integer
… % a is assigned an integer value
r @ (a) . c28 (7) := 'B' % Use indirection operator @
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| Details | Although addressint is called an integer type, it is commonly equivalent to a natural type such as nat4 (for 32-bit machines). Be careful not to confuse addressint with pointer types. In low level languages such as assembler and C, addresses and pointers are the same. In Turing, however, a pointer is a high level concept that is more abstract than a machine address. A Turing pointer is a reference to an object, and the representation of this reference depends upon the implementation. In current Turing implementations, pointers (which are by default checked) are represented as a time stamp (a unique number) together with an address. The time stamp is used to make sure that the pointer actually locates an object. There are also unchecked pointers. An unchecked pointer's internal representation is a machine address. You can use type cheats (a dangerous feature) to translate between addressint and unchecked pointers. This is meaningful in current implementations.
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| See also | the indirection operator @, cheat, explicitIntegerConstant (how to write hexadecimal constants), and pointer type (in particular unchecked pointer type). See also addr, which returns the address of a variable.
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