+
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: +
The old pre-standard bit_vector class is present for
+ backwards compatibility. It is simply a typedef for the
+ vector<bool> specialization.
+
The bitset class has a number of extensions, described in the
+ rest of this item. First, we'll mention that this implementation of
+ bitset<N> 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.
+
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: +
+ 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); +
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). +
The semantics of member function operator[] are not specified
+ in the C++ standard. A long-standing defect report calls for sensible
+ obvious semantics, which are already implemented here: op[]
+ on a const bitset returns a bool, and for a non-const bitset returns a
+ reference (a nested type). However, this implementation does
+ no range-checking on the index argument, which is in keeping with other
+ containers' op[] requirements. The defect report's proposed
+ resolution calls for range-checking to be done. We'll just wait and see...
+
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 prev, respectively:
+
+ size_t _Find_first() const; + size_t _Find_next (size_t prev) const;
The same caveat given for the _Unchecked_* functions applies here also. +