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    <h2>The Answer</h2> <p>The compiler was, in fact, calculating an incorrect address for some of the class members. The culprit turned out to be a <strong><code>#pragma pack 1</code></strong> directive hidden in an obscure header file that was <code>#included</code> in some of the source files.</p> <h2>How I found it</h2> <p>50% persistence, 50% luck, and 10% math skills. :-)</p> <p>I came across a very simple class with few methods and members, most of which were defined in the header file, including:</p> <pre><code>typedef int BOOL; // Legacy, makes my skin crawl; don't ask. BOOL isConnected() { return m_bConnected; }; BOOL m_bConnected; </code></pre> <p>...and the function returned <code>false</code> when I <em>knew</em>&nbsp; <code>m_bConnected</code> was <code>true</code>:</p> <ul> <li>The watch window showed the correct value. Programmatic changes to <code>m_bConnected</code> were reflected in the window.</li> <li>A watch on <code>&amp;m_bConnected</code> showed that it began 8 bytes into the class.</li> <li>The raw memory window showed the correct value. Programmatic changes to <code>m_bConnected</code> were reflected there as well.</li> <li>The 4 bytes before <code>m_bConnected</code> were all <code>0</code>, which I interpreted to be padding.</li> <li>Stepping the debugger through the code clearly showed a return value of <code>false</code>!</li> </ul> <p>So I checked the disassembly window and found this (comments are mine):</p> <pre><code>mov eax,dword ptr [this] ; address of the class instance mov eax,dword ptr [eax+4] ; offset to m_bConnected </code></pre> <p>In other words, the compiler calculated the offset as 4, when it should have been 8.</p> <h2>Aha!</h2> <p>Interestingly, when I removed the definition of <code>isConnected()</code> from the header and placed it into my source file, <em>the address was calculated correctly</em>! That convinced me that it was, indeed, a packing problem, and a search of the code base for <code>#pragma pack</code> quickly identified the culprit, an ancient header file that (legitimately) required alignment on 1-byte boundaries but never reset the packing to the default.</p> <h2>The Fix</h2> <p>The solution was as easy as enclosing the offending header like this:</p> <pre><code>#pragma pack(push) // original code here #pragma pack(pop) </code></pre> <p>Thanks for your interest. And Sara, if you're reading, I'm about to <a href="https://stackoverflow.com/questions/183469/how-do-you-reward-yourself-when-youve-overcome-a-monster-task">dance on my desk</a>!</p>
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