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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>HP/SGI</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.75.2"/><meta name="keywords" content=" ISO C++ , library "/><link rel="home" href="../spine.html" title="The GNU C++ Library"/><link rel="up" href="ext_containers.html" title="Chapter 21. Containers"/><link rel="prev" href="ext_containers.html" title="Chapter 21. Containers"/><link rel="next" href="bk01pt03ch21s03.html" title="Deprecated HP/SGI"/></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">HP/SGI</th></tr><tr><td align="left"><a accesskey="p" href="ext_containers.html">Prev</a> </td><th width="60%" align="center">Chapter 21. Containers</th><td align="right"> <a accesskey="n" href="bk01pt03ch21s03.html">Next</a></td></tr></table><hr/></div><div class="section" title="HP/SGI"><div class="titlepage"><div><div><h2 class="title"><a id="manual.ext.containers.sgi"/>HP/SGI</h2></div></div></div><p>
</p><p>A few extensions and nods to backwards-compatibility have been made with
containers. Those dealing with older SGI-style allocators are dealt with
elsewhere. The remaining ones all deal with bits:
</p><p>The old pre-standard <code class="code">bit_vector</code> class is present for
backwards compatibility. It is simply a typedef for the
<code class="code">vector<bool></code> specialization.
</p><p>The <code class="code">bitset</code> class has a number of extensions, described in the
rest of this item. First, we'll mention that this implementation of
<code class="code">bitset<N></code> is specialized for cases where N number of
bits will fit into a single word of storage. If your choice of N is
within that range (<=32 on i686-pc-linux-gnu, for example), then all
of the operations will be faster.
</p><p>There are
versions of single-bit test, set, reset, and flip member functions which
do no range-checking. If we call them member functions of an instantiation
of "bitset<N>," then their names and signatures are:
</p><pre class="programlisting">
bitset<N>& _Unchecked_set (size_t pos);
bitset<N>& _Unchecked_set (size_t pos, int val);
bitset<N>& _Unchecked_reset (size_t pos);
bitset<N>& _Unchecked_flip (size_t pos);
bool _Unchecked_test (size_t pos);
</pre><p>Note that these may in fact be removed in the future, although we have
no present plans to do so (and there doesn't seem to be any immediate
reason to).
</p><p>The semantics of member function <code class="code">operator[]</code> are not specified
in the C++ standard. A long-standing defect report calls for sensible
obvious semantics, which are already implemented here: <code class="code">op[]</code>
on a const bitset returns a bool, and for a non-const bitset returns a
<code class="code">reference</code> (a nested type). However, this implementation does
no range-checking on the index argument, which is in keeping with other
containers' <code class="code">op[]</code> requirements. The defect report's proposed
resolution calls for range-checking to be done. We'll just wait and see...
</p><p>Finally, two additional searching functions have been added. They return
the index of the first "on" bit, and the index of the first
"on" bit that is after <code class="code">prev</code>, respectively:
</p><pre class="programlisting">
size_t _Find_first() const;
size_t _Find_next (size_t prev) const;</pre><p>The same caveat given for the _Unchecked_* functions applies here also.
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