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    <p>Try this:</p> <pre><code>#ifdef SOMETHING #define foo(x) #else #define foo(x) MyFunction(x) #endif </code></pre> <p>If your function has several arguments, then:</p> <pre><code>#ifdef SOMETHING #define foo(x,y,z) #else #define foo(x,y,z) MyFunction(x,y,z) #endif </code></pre> <p>If your function has a variable number of arguments, then your compiler may support so-called "variadic macros", like this:</p> <pre><code>#ifdef SOMETHING #define foo(...) #else #define foo(...) MyFunction(__VA_ARGS__) #endif </code></pre> <p>The reason which I've seen this kind of thing used in practice is to get rid of logging functions from a release build. However, see also <a href="https://stackoverflow.com/questions/420343/separate-debug-and-release-builds">Separate &#39;debug&#39; and &#39;release&#39; builds?</a> in which people question whether you <em>should</em> even <em>have</em> different builds.</p> <hr> <p>Alternatively, instead of redefining the function call as nothing, Jonathan's comment to this answer suggested doing something like the following:</p> <pre><code>#ifdef SOMETHING #define foo(...) do { if (false) MyFunction(__VA_ARGS__) } while (0) #else #define foo(...) do { if (true) MyFunction(__VA_ARGS__) } while (0) #endif </code></pre> <p>The reasoning for doing this is so that the function call is always compiled (so it won't be left with gratuitous errors like references to deleted variables), but only called when needed: see Kernighan &amp; Pike <a href="http://rads.stackoverflow.com/amzn/click/020161586X" rel="nofollow noreferrer">The Practice of Programming</a> and also the <a href="http://software.gsfc.nasa.gov/assetsbytype.cfm?TypeAsset=Standard" rel="nofollow noreferrer">Goddard Space Flight Center programming standards</a>.</p> <p>From a debug.h file (originating from 1990, and therefore not using <code>__VA_ARGS__</code>):</p> <pre><code>/* ** Usage: TRACE((level, fmt, ...)) ** "level" is the debugging level which must be operational for the output ** to appear. "fmt" is a printf format string. "..." is whatever extra ** arguments fmt requires (possibly nothing). ** The non-debug macro means that the code is validated but never called. ** -- See chapter 8 of 'The Practice of Programming', by Kernighan and Pike. */ #ifdef DEBUG #define TRACE(x) db_print x #else #define TRACE(x) do { if (0) db_print x; } while (0) #endif /* DEBUG */ </code></pre> <p>With C99, there's no longer a need for the double parentheses trick. New code should not use it unless C89 compatibility is an issue.</p>
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    1. POUse #ifdefs and #define to optionally turn a function call into a comment
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    1. COWill this work with a variable number of arguments? e.g. foo(a,b,c)
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    2. COIt will work with a greater-than-one-but-fixed number of arguments. For a variable number of arguments, Google and/or check your compiler documentation for so-called "variadic macros".
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    3. CO@ChrisW If you modify your answer to use a variadic macro, then I _think_ it's exactly what I need :)
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