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<H1> 13.9.2 The Valid Attribute</H1>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal"> The Valid attribute can be used to check the validity
of data produced by unchecked conversion, input, interface to foreign
languages, and the like. </DIV>
<H4 ALIGN=CENTER>Static Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> For a <FONT FACE="Arial, Helvetica">prefix</FONT>
X that denotes a scalar object (after any implicit dereference), the
following attribute is defined: </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>3</FONT></DIV>
<DL Class="Hanging"><DT> X'Valid<DD Class="Hanging">
<A NAME="I4378"></A><A NAME="I4379"></A>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. </DL>
<DIV Class="NotesHeader"><FONT SIZE=-1>NOTES</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<DIV Class="Notes" Style="margin-bottom: 0.4em"><FONT SIZE=-1>19 Invalid
data can be created in the following cases (not counting erroneous or
unpredictable execution): </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>5</FONT></DIV>
<UL Class="NotesBulleted"><FONT SIZE=-1><LI TYPE=DISC>an uninitialized scalar object,</LI></FONT></UL>
<DIV Class="Paranum"><FONT SIZE=-2>6</FONT></DIV>
<UL Class="NotesBulleted"><FONT SIZE=-1><LI TYPE=DISC>the result of an unchecked conversion,</LI></FONT></UL>
<DIV Class="Paranum"><FONT SIZE=-2>7</FONT></DIV>
<UL Class="NotesBulleted"><FONT SIZE=-1><LI TYPE=DISC>input,</LI></FONT></UL>
<DIV Class="Paranum"><FONT SIZE=-2>8</FONT></DIV>
<UL Class="NotesBulleted"><FONT SIZE=-1><LI TYPE=DISC>interface to another language (including machine code),</LI></FONT></UL>
<DIV Class="Paranum"><FONT SIZE=-2>9</FONT></DIV>
<UL Class="NotesBulleted"><FONT SIZE=-1><LI TYPE=DISC>aborting an assignment,</LI></FONT></UL>
<DIV Class="Paranum"><FONT SIZE=-2>10</FONT></DIV>
<UL Class="NotesBulleted"><FONT SIZE=-1><LI TYPE=DISC>disrupting an assignment due to the failure of a language-defined
check (see <A HREF="RM-11-6.html">11.6</A>), and</LI></FONT></UL>
<DIV Class="Paranum"><FONT SIZE=-2>11</FONT></DIV>
<UL Class="NotesBulleted"><FONT SIZE=-1><LI TYPE=DISC>use of an object whose Address has been specified. </LI></FONT></UL>
<DIV Class="Paranum"><FONT SIZE=-2>12</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>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. </FONT></DIV>
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