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4 <meta name="AUTHOR" content="pme@gcc.gnu.org (Phil Edwards)">
5 <meta name="KEYWORDS" content="libstdc++, libstdc++-v3, GCC, g++, STL, SGI">
6 <meta name="DESCRIPTION" content="SGI extensions preserved in libstdc++-v3.">
7 <meta name="GENERATOR" content="vi and eight fingers">
8 <title>SGI extensions to the library in libstdc++-v3</title>
9 <link rel="StyleSheet" href="lib3styles.css">
13 <h1 class="centered"><a name="top">SGI extensions to the library in
16 <p>This page describes the extensions that SGI made to their version of the
17 STL subset of the Standard C++ Library. For a time we
18 <a href="../faq/index.html#5_3">tracked and imported changes and updates
19 from most of the SGI STL</a>, up through their (apparently) final release.
20 Their extensions were mostly preserved.
23 <p>They are listed according to the chapters of the library that they
24 extend (see <a href="../documentation.html#3">the chapter-specific notes</a>
25 for a description). Not every chapter may have extensions, and the
26 extensions may come and go. Also, this page is incomplete because the
27 author is pressed for time. Check back often; the latest change was on
28 $Date: 2001/10/11 18:41:47 $ (UTC).
31 <p>Descriptions range from the scanty to the verbose. You should also check
32 the <a href="../documentation.html#4">generated documentation</a> for notes
33 and comments, especially for entries marked with '*'. For more complete
34 doumentation, see the SGI website. For <em>really</em> complete
35 documentation, buy a copy of Matt Austern's book. *grin*
38 <p>Back to the <a href="howto.html">libstdc++-v3 extensions</a>.
41 <!-- ####################################################### -->
43 <a name="ch20"><h3>Chapter 20</h3></a>
44 <p>The <functional> header contains many additional functors and
45 helper functions, extending section 20.3. They are implemented in the
48 <li><code>identity_element</code> for addition and multiplication. *
49 <li>The functor <code>identity</code>, whose op() returns the argument
51 <li>Composition functors <code>unary_function</code> and
52 <code>binary_function</code>, and their helpers <code>compose1</code>
53 and <code>compose2</code>. *
54 <li><code>select1st</code> and <code>select2nd</code>, to strip pairs. *
55 <li><code>project1st</code> and <code>project2nd</code>. *
56 <li>A set of functors/functions which always return the same result. They
57 are <code>constant_void_fun, constant_binary_fun, constant_unary_fun,
58 constant0, constant1, and constant2. *
59 <li>The class <code>subtractive_rng</code>. *
60 <li>mem_fun adaptor helpers mem_fun1 and mem_fun1_ref are provided for
61 backwards compatibility.
63 <p>20.4.3 is extended with a special version of
64 <code>get_temporary_buffer</code> taking a second argument. The argument
65 is a pointer, which is ignored, but can be used to specify the template
66 type (instead of using explicit function template arguments like the
67 standard version does). That is, in addition to
69 get_temporary_buffer<int>(5);</pre>
72 get_temporary_buffer(5, (int*)0);</pre>
74 <p>A class <code>temporary_buffer</code> is given in stl_tempbuf.h. *
76 <p>The specialized algorithms of section 20.4.4 are extended with
77 <code>uninitialized_copy_n</code>. *
79 <p>Return <a href="howto.html">to the main extensions page</a> or
80 <a href="http://gcc.gnu.org/libstdc++/">to the homepage</a>.
85 <a name="ch23"><h3>Chapter 23</h3></a>
86 <p>A few extensions and nods to backwards-compatibility have been made with
87 containers. Those dealing with older SGI-style allocators are dealt with
88 elsewhere. The remaining ones all deal with bits:
90 <p>The old pre-standard <code>bit_vector</code> class is present for
91 backwards compatibility. It is simply a typedef for the
92 <code>vector<bool></code> specialization.
94 <p>The <code>bitset</code> class has a number of extensions, described in the
95 rest of this item. First, we'll mention that this implementation of
96 <code>bitset<N></code> is specialized for cases where N number of
97 bits will fit into a single word of storage. If your choice of N is
98 within that range (<=32 on i686-pc-linux-gnu, for example), then all
99 of the operations will be faster.
102 versions of single-bit test, set, reset, and flip member functions which
103 do no range-checking. If we call them member functions of an instantiation
104 of "bitset<N>," then their names and signatures are:
106 bitset<N>& _Unchecked_set (size_t pos);
107 bitset<N>& _Unchecked_set (size_t pos, int val);
108 bitset<N>& _Unchecked_reset (size_t pos);
109 bitset<N>& _Unchecked_flip (size_t pos);
110 bool _Unchecked_test (size_t pos);</pre>
111 Note that these may in fact be removed in the future, although we have
112 no present plans to do so (and there doesn't seem to be any immediate
116 The semantics of member function <code>operator[]</code> are not specified
117 in the C++ standard. A long-standing defect report calls for sensible
118 obvious semantics, which are already implemented here: <code>op[]</code>
119 on a const bitset returns a bool, and for a non-const bitset returns a
120 <code>reference</code> (a nested type). However, this implementation does
121 no range-checking on the index argument, which is in keeping with other
122 containers' <code>op[]</code> requirements. The defect report's proposed
123 resolution calls for range-checking to be done. We'll just wait and see...
125 <p>Finally, two additional searching functions have been added. They return
126 the index of the first "on" bit, and the index of the first
127 "on" bit that is after <code>prev</code>, respectively:
129 size_t _Find_first() const;
130 size_t _Find_next (size_t prev) const;</pre>
131 The same caveat given for the _Unchecked_* functions applies here also.
133 <p>Return <a href="howto.html">to the main extensions page</a> or
134 <a href="http://gcc.gnu.org/libstdc++/">to the homepage</a>.
139 <a name="ch24"><h3>Chapter 24</h3></a>
140 <p>24.3.2 describes <code>struct iterator</code>, which didn't exist in the
141 original HP STL implementation (the language wasn't rich enough at the
142 time). For backwards compatibility, base classes are provided which
143 declare the same nested typedefs:
148 <li>bidirectional_iterator
149 <li>random_access_iterator
152 <p>24.3.4 describes iterator operation <code>distance</code>, which takes
153 two iterators and returns a result. It is extended by another signature
154 which takes two iterators and a reference to a result. The result is
155 modified, and the function returns nothing.
157 <p>Return <a href="howto.html">to the main extensions page</a> or
158 <a href="http://gcc.gnu.org/libstdc++/">to the homepage</a>.
163 <a name="ch25"><h3>Chapter 25</h3></a>
164 <p>25.1.6 (count, count_if) is extended with two more versions of count
165 and count_if. The standard versions return their results. The
166 additional signatures return void, but take a final parameter by
167 reference to which they assign their results, e.g.,
169 void count (first, last, value, n);</pre>
171 <p>25.2 (mutating algorithms) is extended with two families of signatures,
172 random_sample and random_sample_n.
174 <p>25.2.1 (copy) is extended with
176 copy_n (_InputIter first, _Size count, _OutputIter result);</pre>
177 which copies the first 'count' elements at 'first' into 'result'.
179 <p>25.3 (sorting 'n' heaps 'n' stuff) is extended with some helper
180 predicates. Look in the doxygen-generated pages for notes on these.
182 <li><code>is_heap</code> tests whether or not a range is a heap.
183 <li><code>is_sorted</code> tests whether or not a range is sorted in
187 <p>25.3.8 (lexigraphical_compare) is extended with
189 lexicographical_compare_3way(_InputIter1 first1, _InputIter1 last1,
190 _InputIter2 first2, _InputIter2 last2)</pre>
193 <p>Return <a href="howto.html">to the main extensions page</a> or
194 <a href="http://gcc.gnu.org/libstdc++/">to the homepage</a>.
199 <a name="ch26"><h3>Chapter 26</h3></a>
200 <p>26.4, the generalized numeric operations such as accumulate, are extended
201 with the following functions:
204 power (x, n, moniod_operation);</pre>
205 Returns, in FORTRAN syntax, "x ** n" where n>=0. In the
206 case of n == 0, returns the <a href="#ch20">identity element</a> for the
207 monoid operation. The two-argument signature uses multiplication (for
208 a true "power" implementation), but addition is supported as well.
209 The operation functor must be associative.
211 <p>The <code>iota</code> function wins the award for Extension With the
212 Coolest Name. It "assigns sequentially increasing values to a range.
213 That is, it assigns value to *first, value + 1 to *(first + 1) and so
214 on." Quoted from SGI documentation.
216 void iota(_ForwardIter first, _ForwardIter last, _Tp value);</pre>
218 <p>Return <a href="howto.html">to the main extensions page</a> or
219 <a href="http://gcc.gnu.org/libstdc++/">to the homepage</a>.
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228 Comments and suggestions are welcome, and may be sent to
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