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26 <div class=
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27 <a name=
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28 positive with -Wmaybe-uninitialized
</a>
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31 Sometimes on GCC compilers below version
5.1 you may get an -Wmaybe-uninitialized
32 warning when copiling with option -
02 on a perfectly valid
<code class=
"computeroutput"><span class=
"identifier">boost
</span><span class=
"special">::
</span><span class=
"identifier">optional
</span></code> usage. For instance in this
35 <pre class=
"programlisting"><span class=
"preprocessor">#include
</span> <span class=
"special"><</span><span class=
"identifier">boost
</span><span class=
"special">/
</span><span class=
"identifier">optional
</span><span class=
"special">.
</span><span class=
"identifier">hpp
</span><span class=
"special">></span>
37 <span class=
"identifier">boost
</span><span class=
"special">::
</span><span class=
"identifier">optional
</span><span class=
"special"><</span><span class=
"keyword">int
</span><span class=
"special">></span> <span class=
"identifier">getitem
</span><span class=
"special">();
</span>
39 <span class=
"keyword">int
</span> <span class=
"identifier">main
</span><span class=
"special">(
</span><span class=
"keyword">int
</span> <span class=
"identifier">argc
</span><span class=
"special">,
</span> <span class=
"keyword">const
</span> <span class=
"keyword">char
</span> <span class=
"special">*[])
</span>
40 <span class=
"special">{
</span>
41 <span class=
"identifier">boost
</span><span class=
"special">::
</span><span class=
"identifier">optional
</span><span class=
"special"><</span><span class=
"keyword">int
</span><span class=
"special">></span> <span class=
"identifier">a
</span> <span class=
"special">=
</span> <span class=
"identifier">getitem
</span><span class=
"special">();
</span>
42 <span class=
"identifier">boost
</span><span class=
"special">::
</span><span class=
"identifier">optional
</span><span class=
"special"><</span><span class=
"keyword">int
</span><span class=
"special">></span> <span class=
"identifier">b
</span><span class=
"special">;
</span>
44 <span class=
"keyword">if
</span> <span class=
"special">(
</span><span class=
"identifier">argc
</span> <span class=
"special">></span> <span class=
"number">0</span><span class=
"special">)
</span>
45 <span class=
"identifier">b
</span> <span class=
"special">=
</span> <span class=
"identifier">argc
</span><span class=
"special">;
</span>
47 <span class=
"keyword">if
</span> <span class=
"special">(
</span><span class=
"identifier">a
</span> <span class=
"special">!=
</span> <span class=
"identifier">b
</span><span class=
"special">)
</span>
48 <span class=
"keyword">return
</span> <span class=
"number">1</span><span class=
"special">;
</span>
50 <span class=
"keyword">return
</span> <span class=
"number">0</span><span class=
"special">;
</span>
51 <span class=
"special">}
</span>
54 This is a bug in the compiler. As a workaround (provided in
<a href=
"http://stackoverflow.com/questions/21755206/how-to-get-around-gcc-void-b-4-may-be-used-uninitialized-in-this-funct" target=
"_top">this
55 Stack Overflow question
</a>) use the following way of initializing
56 an optional containing no value:
58 <pre class=
"programlisting"><span class=
"identifier">boost
</span><span class=
"special">::
</span><span class=
"identifier">optional
</span><span class=
"special"><</span><span class=
"keyword">int
</span><span class=
"special">></span> <span class=
"identifier">b
</span> <span class=
"special">=
</span> <span class=
"identifier">std
</span><span class=
"special">::
</span><span class=
"identifier">make_optional
</span><span class=
"special">(
</span><span class=
"keyword">false
</span><span class=
"special">,
</span> <span class=
"keyword">int
</span><span class=
"special">());
</span>
61 This is obviously redundant, but makes the warning disappear.
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2007 Fernando Luis Cacciola Carballal
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2016 Andrzej Krzemie
ński
<p>
67 Distributed under the Boost Software License, Version
1.0. (See accompanying
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<a href=
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