1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
|
<HTML>
<!--
-- Copyright (c) 1996-1999
-- Silicon Graphics Computer Systems, Inc.
--
-- Permission to use, copy, modify, distribute and sell this software
-- and its documentation for any purpose is hereby granted without fee,
-- provided that the above copyright notice appears in all copies and
-- that both that copyright notice and this permission notice appear
-- in supporting documentation. Silicon Graphics makes no
-- representations about the suitability of this software for any
-- purpose. It is provided "as is" without express or implied warranty.
--
-- Copyright (c) 1994
-- Hewlett-Packard Company
--
-- Permission to use, copy, modify, distribute and sell this software
-- and its documentation for any purpose is hereby granted without fee,
-- provided that the above copyright notice appears in all copies and
-- that both that copyright notice and this permission notice appear
-- in supporting documentation. Hewlett-Packard Company makes no
-- representations about the suitability of this software for any
-- purpose. It is provided "as is" without express or implied warranty.
--
-->
<Head>
<Title>get_temporary_buffer</Title>
<!-- Generated by htmldoc -->
</HEAD>
<BODY BGCOLOR="#ffffff" LINK="#0000ee" TEXT="#000000" VLINK="#551a8b"
ALINK="#ff0000">
<IMG SRC="CorpID.gif"
ALT="SGI" HEIGHT="43" WIDTH="151">
<!--end header-->
<BR Clear>
<H1>get_temporary_buffer</H1>
<Table CellPadding=0 CellSpacing=0 width=100%>
<TR>
<TD Align=left><Img src = "allocators.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD>
<TD Align=right><Img src = "function.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD>
</TR>
<TR>
<TD Align=left VAlign=top><b>Category</b>: allocators</TD>
<TD Align=right VAlign=top><b>Component type</b>: function</TD>
</TR>
</Table>
<h3>Prototype</h3>
<pre>
template <class T>
<A href="pair.html">pair</A><T*, ptrdiff_t> get_temporary_buffer(ptrdiff_t len, T*);
</pre>
<h3>Description</h3>
Some algorithms, such as <tt><A href="stable_sort.html">stable_sort</A></tt> and <tt><A href="inplace_merge.html">inplace_merge</A></tt>,
are <i>adaptive</i>: they attempt to use extra temporary memory to store
intermediate results, and their run-time complexity is better if that
extra memory is available.
<P>
The first argument to <tt>get_temporary_buffer</tt> specifies the
requested size of the temporary buffer, and the second specifies
the type of object that will be stored in the buffer. That is,
<tt>get_temporary_buffer(len, (T*) 0)</tt> requests a buffer that is
aligned for objects of type <tt>T</tt> and that is large enough to hold
<tt>len</tt> objects of type <tt>T</tt>. <A href="#1">[1]</A>
<P>
The return value of <tt>get_temporary_buffer</tt> is a <A href="pair.html">pair</A> <tt>P</tt> whose
first component is a pointer to the temporary buffer and whose second
argument indicates how large the buffer is: the buffer pointed to by
<tt>P.first</tt> is large enough to hold <tt>P.second</tt> objects of type <tt>T</tt>.
<tt>P.second</tt> is greater than or equal to <tt>0</tt> <A href="#2">[2]</A>, and less than or equal
to <tt>len</tt> <A href="#1">[1]</A>. Note that <tt>P.first</tt> is a pointer to uninitialized
memory, rather than to actual objects of type <tt>T</tt>; this memory can be
initialized using <tt><A href="uninitialized_copy.html">uninitialized_copy</A></tt>, <tt><A href="uninitialized_fill.html">uninitialized_fill</A></tt>,
or <tt><A href="uninitialized_fill_n.html">uninitialized_fill_n</A></tt>.
<P>
As the name suggests, <tt>get_temporary_buffer</tt> should only be used to
obtain temporary memory. If a function allocates memory using
<tt>get_temporary_buffer</tt>, then it must deallocate that memory, using
<tt><A href="return_temporary_buffer.html">return_temporary_buffer</A></tt> <A href="#3">[3]</A>, before it returns.
<P>
<b>Note:</b> <tt>get_temporary_buffer</tt> and <tt><A href="return_temporary_buffer.html">return_temporary_buffer</A></tt> are
only provided for backward compatibility. If you are writing new
code, you should instead use the <tt><A href="temporary_buffer.html">temporary_buffer</A></tt> class.
<h3>Definition</h3>
Defined in the standard header <A href="memory">memory</A>, and in the nonstandard
backward-compatibility header <A href="algo.h">algo.h</A>.
<h3>Requirements on types</h3>
<h3>Preconditions</h3>
<UL>
<LI>
<tt>len</tt> is greater than <tt>0</tt>.
</UL>
<h3>Complexity</h3>
<h3>Example</h3>
<pre>
int main()
{
pair<int*, ptrdiff_t> P = get_temporary_buffer(10000, (int*) 0);
int* buf = P.first;
ptrdiff_t N = P.second;
<A href="uninitialized_fill_n.html">uninitialized_fill_n</A>(buf, N, 42);
int* result = <A href="find_if.html">find_if</A>(buf, buf + N, <A href="binder2nd.html">bind2nd</A>(<A href="not_equal_to.html">not_equal_to</A><int>(), 42));
assert(result == buf + N);
<A href="return_temporary_buffer.html">return_temporary_buffer</A>(buf);
}
</pre>
<h3>Notes</h3>
<P><A name="1">[1]</A>
The argument <tt>len</tt> is a request, rather than a requirement. The
intention is that <tt>get_temporary_buffer</tt> will return as large a buffer
as can be allocated without hurting performance. Note that
determining this maximum size is quite difficult: it
depends on cache size, physical versus virtual memory,
heap fragmentation, and so on. A good implementation of
<tt>get_temporary_buffer</tt> must be nonportable.
<P><A name="2">[2]</A>
If <tt>P.second</tt> is 0, this means that <tt>get_temporary_buffer</tt>
was unable to allocate a temporary buffer at all. In that case,
<tt>P.first</tt> is a null pointer.
<P><A name="3">[3]</A>
It is unspecified whether <tt>get_temporary_buffer</tt> is implemented
using <tt>malloc</tt>, or <tt>::operator new</tt>, or some other method. The only
portable way to return memory that was allocated using <tt>get_temporary_buffer</tt>
is to use <tt><A href="return_temporary_buffer.html">return_temporary_buffer</A></tt>.
<h3>See also</h3>
<tt><A href="temporary_buffer.html">temporary_buffer</A></tt>, <tt><A href="return_temporary_buffer.html">return_temporary_buffer</A></tt>, <A href="Allocators.html">Allocators</A>
<!--start footer-->
<HR SIZE="6">
<A href="http://www.sgi.com/"><IMG SRC="surf.gif" HEIGHT="54" WIDTH="54"
ALT="[Silicon Surf]"></A>
<A HREF="index.html"><IMG SRC="stl_home.gif"
HEIGHT="54" WIDTH="54" ALT="[STL Home]"></A>
<BR>
<FONT SIZE="-2">
<A href="http://www.sgi.com/Misc/sgi_info.html" TARGET="_top">Copyright ©
1999 Silicon Graphics, Inc.</A> All Rights Reserved.</FONT>
<FONT SIZE="-3"><a href="http://www.sgi.com/Misc/external.list.html" TARGET="_top">TrademarkInformation</A>
</FONT>
<P>
</BODY>
</HTML>
|
