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4 </p><p>A few extensions and nods to backwards-compatibility have been made with
5 containers. Those dealing with older SGI-style allocators are dealt with
6 elsewhere. The remaining ones all deal with bits:
7 </p><p>The old pre-standard <code class="code">bit_vector</code> class is present for
8 backwards compatibility. It is simply a typedef for the
9 <code class="code">vector<bool></code> specialization.
10 </p><p>The <code class="code">bitset</code> class has a number of extensions, described in the
11 rest of this item. First, we'll mention that this implementation of
12 <code class="code">bitset<N></code> is specialized for cases where N number of
13 bits will fit into a single word of storage. If your choice of N is
14 within that range (<=32 on i686-pc-linux-gnu, for example), then all
15 of the operations will be faster.
17 versions of single-bit test, set, reset, and flip member functions which
18 do no range-checking. If we call them member functions of an instantiation
19 of "bitset<N>," then their names and signatures are:
20 </p><pre class="programlisting">
21 bitset<N>& _Unchecked_set (size_t pos);
22 bitset<N>& _Unchecked_set (size_t pos, int val);
23 bitset<N>& _Unchecked_reset (size_t pos);
24 bitset<N>& _Unchecked_flip (size_t pos);
25 bool _Unchecked_test (size_t pos);
26 </pre><p>Note that these may in fact be removed in the future, although we have
27 no present plans to do so (and there doesn't seem to be any immediate
29 </p><p>The semantics of member function <code class="code">operator[]</code> are not specified
30 in the C++ standard. A long-standing defect report calls for sensible
31 obvious semantics, which are already implemented here: <code class="code">op[]</code>
32 on a const bitset returns a bool, and for a non-const bitset returns a
33 <code class="code">reference</code> (a nested type). However, this implementation does
34 no range-checking on the index argument, which is in keeping with other
35 containers' <code class="code">op[]</code> requirements. The defect report's proposed
36 resolution calls for range-checking to be done. We'll just wait and see...
37 </p><p>Finally, two additional searching functions have been added. They return
38 the index of the first "on" bit, and the index of the first
39 "on" bit that is after <code class="code">prev</code>, respectively:
40 </p><pre class="programlisting">
41 size_t _Find_first() const;
42 size_t _Find_next (size_t prev) const;</pre><p>The same caveat given for the _Unchecked_* functions applies here also.
43 </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ext_containers.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ext_containers.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="bk01pt03ch21s03.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 21. Containers </td><td width="20%" align="center"><a accesskey="h" href="../spine.html">Home</a></td><td width="40%" align="right" valign="top"> Deprecated HP/SGI</td></tr></table></div></body></html>