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<title>Long double - GNU Scientific Library -- Reference Manual</title>
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<h3 class="section">2.6 Long double</h3>
<p><a name="index-long-double-37"></a>The extended numerical type <code>long double</code> is part of the ANSI C
standard and should be available in every modern compiler. However, the
precision of <code>long double</code> is platform dependent, and this should
be considered when using it. The IEEE standard only specifies the
minimum precision of extended precision numbers, while the precision of
<code>double</code> is the same on all platforms.
<p>In some system libraries the <code>stdio.h</code> formatted input/output
functions <code>printf</code> and <code>scanf</code> are not implemented correctly
for <code>long double</code>. Undefined or incorrect results are avoided by
testing these functions during the <code>configure</code> stage of library
compilation and eliminating certain GSL functions which depend on them
if necessary. The corresponding line in the <code>configure</code> output
looks like this,
<pre class="example"> checking whether printf works with long double... no
</pre>
<p class="noindent">Consequently when <code>long double</code> formatted input/output does not
work on a given system it should be impossible to link a program which
uses GSL functions dependent on this.
<p>If it is necessary to work on a system which does not support formatted
<code>long double</code> input/output then the options are to use binary
formats or to convert <code>long double</code> results into <code>double</code> for
reading and writing.
<hr>The GNU Scientific Library - a free numerical library licensed under the GNU GPL<br>Back to the <a href="/software/gsl/">GNU Scientific Library Homepage</a></body></html>
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