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POAvoiding repeated replacements in the C pre-processor
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copied!<p>I've been hacking on a program that itself creates simulation programs in <strong>C</strong>. The user specifies the top-level design, and this programs inserts small C-fragments and a helluvalot glue-code (a few thousand lines).</p> <p>It does local naming by <code>#defines</code>:</p> <pre><code>#define x local_x #define vx local_vx /* user code that uses x, ex */ vx = x / 2 #undef vx #undef x </code></pre> <p>This approx expands to the following:</p> <pre><code>local_vx = local_x / 2 </code></pre> <p>BUT if I use structs for the <code>local_*</code>-variables (optimize away having to pass 11 variables to every single function...):</p> <pre><code>#define x local->position.x #define vx local->velocity.x vx = x / 2 #undef vx #undef x </code></pre> <p>Which gets expanded to</p> <pre><code>local->velocity.x = local->position.x </code></pre> <p>And - here's the problem - the <code>x</code> in the velocity gets expanded again:</p> <pre><code>local->velocity.local->position.x = local->position.x </code></pre> <p>I can't put parenthesis around, as it is not allowed to assign to the variables (<code>(x) = 1</code> is illegal <strong>C</strong>, unfortunately...). Any hints?</p> <p><strong>Update:</strong> The generated simulations generally weigh in around 15 to 20.000 LOC, and there are roughly ten years worth of simulations to be backwards compatible with. Alas, <em>simply</em> renaming anything is not simple at all... As there does not seem to be any easy way to get around this particular problem without some major re-engineering (I thought I'd missed some particularities of the <strong>C</strong> pre-processor), I've chosen to take a step back and see what other options I have.</p>

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