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PODelphi: Undefined record variable
 

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  1. PODelphi: Undefined record variable
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    <p>I have defined a <code>TCGTable</code> record type with the following structure:</p> <pre><code>type TCGTable = record x : array [1 .. MAX_POINTS] of Single; y : array [1 .. MAX_POINTS] of Single; end; </code></pre> <p>I have declared a <code>TCGTable</code> variable <code>CGTable</code>. </p> <p>The variable <code>CGTable</code> is assigned a particular constant <code>TCGTable</code> record value if that record meets several runtime conditions.</p> <p>If no constant <code>TCGTable</code> record meets these conditions, <code>CGTable</code> should be undefined. </p> <p>Is there a Delphi 2010 built-in value I can assign to <code>CGTable</code> to indicate that it is undefined? I have tried using the values <code>nil</code> and <code>null</code>, but both of these seem to be valid only for pointer or variant types. The source will not compile with these values assigned to <code>CGTable</code>.</p> <p>I would like to inspect the variable <code>CGTable</code> to determine its validity instead of, for example, maintaining some additional boolean validity flag.</p> <p>The only workarounds I can determine are:</p> <p>a) Change the type of <code>CGTable</code> to a <code>TCGTable</code> pointer (<code>CGTable : ^TCGTable;</code>), which would then allow me to compare <code>CGTable</code> to the <code>nil</code> value.</p> <p>b) Define some constant <code>TCGTable</code> record to act as an "invalid" record. I would then compare <code>CGTable</code> against this "invalid" record.</p> <p>Any suggestions on how to approach this? Thanks</p>
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    1. COApproach (b) was my first idea, but you must be sure that there will never be a *valid* `TCGTable` that looks like that.
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      1. USAndreas Rejbrand
    2. COWith approach (b) you have to check MAX_POINTS * 2 * SizeOf(Single) bytes to determine whether a TCGTable is valid, though.
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    3. COYou can have a validity flag and inspect the record itself at the same time. That is you can include the flag in the record.
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      1. USSertac Akyuz
 

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