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13.9.2 The Valid Attribute

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

For a prefix X that denotes a scalar object (after any implicit dereference), the following attribute is defined:

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.

NOTES

(19) Invalid data can be created in the following cases (not counting erroneous or unpredictable execution):

• an uninitialized scalar object,

• the result of an unchecked conversion,

• input,

• interface to another language (including machine code),

• aborting an assignment,

• disrupting an assignment due to the failure of a language-defined check (see 11.6), and

• use of an object whose Address has been specified.

(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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