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    <p>Macros don't respect scoping rules and operate at the textual level, as opposed to the syntax level. From this arise a number of pitfalls that can lead to strange, difficult to isolate bugs.</p> <p>Consider the following well-known example:</p> <pre><code>#define max(a, b) ((a) &lt; (b) ? (b) : (a)) ⋮ int i = max(i++, j++); </code></pre> <p>The preferred alternative in this case is a function template:</p> <pre><code>template &lt;typename T&gt; T max(const T &amp; a, const T &amp; b) { return a &lt; b ? b : a; } </code></pre> <p>Here's another case that leads to subtle problems:</p> <pre><code>#define CHECK_ERROR(ret, msg) \ if (ret != STATUS_OK) { \ fprintf(stderr, "Error %d: %s\n", ret, msg); \ exit(1); \ } ⋮ if (ready) CHECK_ERROR(try_send(packet), "Failed to send"); else enqueue(packet); </code></pre> <p>You might think that the solution is as simple as wrapping the contents of <code>CHECK_ERROR</code> in <code>{ … }</code>, but this won't compile due to the <code>;</code> before the <code>else</code>.</p> <p>To avoid the above problem (the <code>else</code> attaching to <code>CHECK_ERROR</code>'s <code>if</code> instead of the outer <code>if</code>), one should wrap such macros in <code>do … while (false)</code> as follows:</p> <pre><code>#define CHECK_ERROR(ret, msg) \ do { \ if (ret != STATUS_OK) { \ fprintf(stderr, "Error %d: %s\n", ret, msg); \ exit(1); \ } \ while (false) </code></pre> <p>This has no effect on the meaning of the macro, but ensures that the entire block is always treated as a single statement and doesn't interact in surprising ways with <code>if</code> statements.</p> <p>Long story short, macros are hazardous at many levels and should thus be used only as a last resort.</p>
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    1. POWhy should I avoid macros in C++?
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    1. COBut it does the same, right? Why not macro instead of a template
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    2. CO@Davlog: Think about how the macro expands: `max(i++, j++)` ⇒ `((i++) < (j++) ? (j++) : (i++))`. Note how whichever variable is the higher ends up being incremented twice. This is the essential problem with the fact that macros perform textual substitutions.
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