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13.9.2 The Valid Attribute
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The Valid attribute can be used to check the validity
of data produced by unchecked conversion, input, interface to foreign
languages, and the like.
Static Semantics
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For a prefix
X that denotes a scalar object (after any implicit dereference), the
following attribute is defined:
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- X'Valid
-
Yields True if and only if the
object denoted by X is normal and has a valid representation. The value
of this attribute is of the predefined type Boolean.
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19 Invalid
data can be created in the following cases (not counting erroneous or
unpredictable execution):
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- an uninitialized
scalar object,
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- the result of
an unchecked conversion,
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- interface to
another language (including machine code),
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- disrupting an
assignment due to the failure of a language-defined check (see 11.6),
and
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- use of an object
whose Address has been specified.
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20 X'Valid is not considered
to be a read of X; hence, it is not an error to check the validity of
invalid data.
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