📄 get_temporary_buffer.html
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<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. 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It is provided "as is" without express or implied warranty. -- --><Head><Title>get_temporary_buffer</Title><!-- Generated by htmldoc --></HEAD><BODY TEXT="#000000" LINK="#006600" ALINK="#003300" VLINK="#7C7F87" BGCOLOR="#FFFFFF"><A HREF="/"><IMG SRC="/images/common/sgilogo_small.gif" ALT="SGI Logo" WIDTH="80" HEIGHT="72" BORDER="0"></A><P><!--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 storeintermediate results, and their run-time complexity is better if thatextra memory is available. <P>The first argument to <tt>get_temporary_buffer</tt> specifies the requested size of the temporary buffer, and the second specifiesthe type of object that will be stored in the buffer. That is,<tt>get_temporary_buffer(len, (T*) 0)</tt> requests a buffer that isaligned 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> whosefirst component is a pointer to the temporary buffer and whose secondargument 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 equalto <tt>len</tt> <A href="#1">[1]</A>. Note that <tt>P.first</tt> is a pointer to uninitializedmemory, rather than to actual objects of type <tt>T</tt>; this memory can beinitialized 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 toobtain 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> areonly provided for backward compatibility. If you are writing newcode, 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 nonstandardbackward-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. Theintention is that <tt>get_temporary_buffer</tt> will return as large a bufferas can be allocated without hurting performance. Note thatdetermining 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 implementedusing <tt>malloc</tt>, or <tt>::operator new</tt>, or some other method. The onlyportable 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 --><!-- Footer Begins --><STYLE TYPE="text/css"><!--TD.footer, TD.footer A{ font-family: Arial, helvetica, sans-serif; font-size: 8pt;}A.home {font-family: Arial, helvetica, sans-serif;}--></STYLE><P><A CLASS="home" HREF="index.html">STL Home</A><P><TABLE WIDTH="600" CELLPADDING="0" CELLPADDING="0" BORDER="0"> <TR> <TD ALIGN="RIGHT" CLASS="footer"><A HREF="/company_info/terms.html" TARGET="_top">terms of use</A> | <A HREF="/company_info/privacy.html" TARGET="_top">privacy policy</A></TD> <TD ALIGN="CENTER" CLASS="footer"> | </TD> <TD ALIGN="LEFT" CLASS="footer"><A HREF="/cgi-bin/feedback/" TARGET="_top">contact us</A></TD> </TR><TR> <TD ALIGN="RIGHT" CLASS="footer">Copyright © 1993-2003 Silicon Graphics, Inc. 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