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    <blockquote> <p>I always get 0 from Integers and false from Booleans for all record members. </p> <p>I tried turning various compiler options (debugging, optimizations, etc.) on and off, but there was no difference. All my record members are being initialized.</p> <p>What am I missing?</p> </blockquote> <p>Well, apart from your test using global instead of local variables: the important thing that you are missing is the distinction between variables that <em><strong>coincidentally appear</strong></em> to be initialised, and variables that <em><strong>actally are</strong></em> initialised.<br> <strong>BTW</strong>: This is the reason programmers who don't check their warnings make the common mistake of assuming their poorly written code is behaving correctly when the few tests they do; happen to have 0 and False defaults.... <code>Want To Buy: random initialisation of local variables for debug builds.</code></p> <p>Consider the following variation on your test code:</p> <pre><code>program LocalVarInit; {$APPTYPE CONSOLE} procedure DoTest; var I, J, K, L, M, N: Integer; S: string; begin Writeln('Test default values'); Writeln('Numbers: ', I:10, J:10, K:10, L:10, M:10, N:10); Writeln('S: ', S); I := I + 1; J := J + 2; K := K + 3; L := L + 5; M := M + 8; N := N + 13; S := 'Hello'; Writeln('Test modified values'); Writeln('Numbers: ', I:10, J:10, K:10, L:10, M:10, N:10); Writeln('S: ', S); Writeln(''); Writeln(''); end; begin DoTest; DoTest; Readln; end. </code></pre> <p>With the following sample output:</p> <pre><code>Test default values Numbers: 4212344 1638280 4239640 4239632 0 0 S: Test modified values Numbers: 4212345 1638282 4239643 4239637 8 13 //Local vars on stack at end of first call to DoTest S: Hello Test default values Numbers: 4212345 1638282 4239643 4239637 8 13 //And the values are still there on the next call S: Test modified values Numbers: 4212346 1638284 4239646 4239642 16 26 S: Hello </code></pre> <p><strong>Notes</strong></p> <ul> <li>The example works best if you compile with optimisation off. Otherwise, if you have optimisation on: <ul> <li>Some local vars will be manipulated in CPU registers.</li> <li>And if you view the CPU stack while stepping through the code you'll note for example that <code>I := I + 1</code> doesn't even modify the stack. So obviously the change cannot be carried through.</li> </ul></li> <li>You could experiment with different calling conventions to see how that affects things.</li> <li>You can also test the effect of setting the local vars to zero instead of incrementing them.</li> <li>This illustrates how you are entirely dependent on what found its way onto the stack <em>before</em> your method was called.</li> </ul>
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    1. USCraig Young
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