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<h3 class="section">2.7 Portability functions</h3>
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<p>To help in writing portable applications GSL provides some
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implementations of functions that are found in other libraries, such as
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the BSD math library. You can write your application to use the native
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versions of these functions, and substitute the GSL versions via a
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preprocessor macro if they are unavailable on another platform.
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<p>For example, after determining whether the BSD function <code>hypot</code> is
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available you can include the following macro definitions in a file
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<samp><span class="file">config.h</span></samp> with your application,
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<pre class="example"> /* Substitute gsl_hypot for missing system hypot */
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#define hypot gsl_hypot
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<p class="noindent">The application source files can then use the include command
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<code>#include <config.h></code> to replace each occurrence of <code>hypot</code> by
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<code>gsl_hypot</code> when <code>hypot</code> is not available. This substitution
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can be made automatically if you use <code>autoconf</code>, see <a href="Autoconf-Macros.html#Autoconf-Macros">Autoconf Macros</a>.
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<p>In most circumstances the best strategy is to use the native versions of
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these functions when available, and fall back to GSL versions otherwise,
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since this allows your application to take advantage of any
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platform-specific optimizations in the system library. This is the
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strategy used within GSL itself.
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