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<H2>gslice</H2>
<P><B>Library:</B>&nbsp;&nbsp;<A HREF="2-10.html">Numerics</A></P>
<PRE><HR><B><I>Does not inherit</I></B><HR></PRE>
<UL>
<LI><A HREF="#sec1">Local Index</A></LI>
<LI><A HREF="#sec2">Summary</A></LI>
<LI><A HREF="#sec3">Synopsis</A></LI>
<LI><A HREF="#sec4">Description</A></LI>
<LI><A HREF="#sec5">Interface</A></LI>
<LI><A HREF="#sec6">Constructors</A></LI>
<LI><A HREF="#sec7">Accessors</A></LI>
<LI><A HREF="#sec8">Example</A></LI>
<LI><A HREF="#sec9">See Also</A></LI>
<LI><A HREF="#sec10">Standards Conformance</A></LI>
</UL>
<A NAME="sec1"><H3>Local Index</H3></A>
<H4>Members</H4>
<UL><TABLE CELLPADDING=3>
<TR><TD VALIGN=top>
<A HREF="#idx647">gslice()</A><BR>
</TD>
<TD VALIGN=top><A HREF="#idx651">size()</A><BR>
</TD>
<TD VALIGN=top><A HREF="#idx650">start()</A><BR>
</TD>
<TD VALIGN=top><A HREF="#idx652">stride()</A><BR>
</TD></TR>
</TABLE></UL>
<A NAME="sec2"><H3>Summary</H3></A>
<P>A numeric array class used to represent a generalized slice from an array</P>
<A NAME="sec3"><H3>Synopsis</H3></A>
<PRE>#include &lt;valarray&gt;
namespace std {
class gslice;
}
</PRE>
<A NAME="sec4"><H3>Description</H3></A>
<P><B><I>gslice</I></B> represents a generalized slice from an array. A generalized slice contains a starting index, a set of lengths, and a set of strides. The number of lengths and strides must be equal. Together the lengths and strides allow a slice from a multiple dimension array (with the dimension equal to the number of strides) to be represented on a one-dimensional <B><I><A HREF="valarray.html">valarray</A></I></B>. The <B><I>gslice</I></B> maps a set of <SAMP>n</SAMP> indices <SAMP>(ij)</SAMP>, where <SAMP>n</SAMP> is equal to the number of strides, to a single index <SAMP>k</SAMP>. </P>
<P>When applied to a <B><I><A HREF="valarray.html">valarray</A></I></B> using the <B><I>gslice</I></B> subscript operator (see <B><I>valarray</I></B>), a <B><I>gslice</I></B> produces a <B><I><A HREF="gslice-array.html">gslice_array</A></I></B>. The <B><I>gslice_array</I></B> class creates a view into the original <B><I>valarray</I></B> that is tailored to match parameters of the <B><I>gslice</I></B>. The elements in a <B><I>gslice_array</I></B> are references to the elements in the original array. </P>
<A NAME="sec5"><H3>Interface</H3></A>
<UL><PRE>namespace std{
class gslice {
public:
// constructors
gslice();
gslice(size_t, const valarray&lt;size_t&gt;&amp;,
const valarray&lt;size_t&gt;&amp;);
gslice(const gslice&amp;);
// Accessors
size_t start() const;
valarray&lt;size_t&gt; size() const;
valarray&lt;size_t&gt; stride() const;
};
}
</PRE></UL>
<A NAME="sec6"><H3>Constructors</H3></A>
<A NAME="idx647"></A><PRE><B>gslice</B>();</PRE>
<UL>
<P>Default constructor creates a <B><I>gslice</I></B> specifying no elements. </P>
</UL>
<A NAME="idx648"></A><PRE><B>gslice</B>(size_t start, const valarray&lt;size_t&gt;&amp; length,
const valarray&lt;size_t&gt;&amp; stride);</PRE>
<UL>
<P>Creates a <B><I>gslice</I></B> with starting index, length, and stride as indicated by the arguments. </P>
</UL>
<A NAME="idx649"></A><PRE><B>gslice</B>(const gslice&amp;)</PRE>
<UL>
<P>Creates a <B><I>gslice</I></B> with starting index, length, and stride as indicated by the slice argument. </P>
</UL>
<A NAME="sec7"><H3>Accessors</H3></A>
<A NAME="idx650"></A><PRE>size_t <B>start</B>() const;</PRE>
<UL>
<P>Returns the starting index of the <B><I>gslice</I></B>.</P>
</UL>
<A NAME="idx651"></A><PRE>valarray&lt;size_t&gt; <B>size</B>() const;</PRE>
<UL>
<P>Returns a <SAMP>valarray&lt;size_t&gt;</SAMP> containing the lengths of the <B><I>gslice</I></B>.</P>
</UL>
<A NAME="idx652"></A><PRE>valarray&lt;size_t&gt; <B>stride</B>() const;</PRE>
<UL>
<P>Returns a <SAMP>valarray&lt;size_t&gt;</SAMP> containing the strides of the <B><I>gslice</I></B>. </P>
</UL>
<A NAME="sec8"><H3>Example</H3></A>
<UL><PRE>//
// gslice.cpp
//
#include &lt;valarray.h&gt; // Includes valarray and provides
// stream inserter.
typedef std::valarray&lt;int&gt; valarray_t;
typedef std::valarray&lt;size_t&gt; selector_t;
int main(void) {
// Create a valarray of ints.
valarray_t::value_type ibuf[27] =
{ 0, 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 };
valarray_t vi(ibuf, 27);
// Create length and stride valarray
selector_t::value_type length_buf[3] = {3,3,3};
selector_t::value_type stride_buf[3] = {9,3,1};
selector_t length_val(length_buf, 3);
selector_t stride_val(stride_buf, 3);
// Print out the valarray&lt;int&gt;.
std::cout &lt;&lt; "original valarray vi\n\n" &lt;&lt; vi &lt;&lt; "\n\n";
// Print out all three dimensions (the entire valarray).
std::cout &lt;&lt; "vi[gslice(0,{3,3,3},{9,3,1})]\n\n"
&lt;&lt; vi[std::gslice(0,length_val,stride_val)]
&lt;&lt; "\n\n";
// Print a two dimensional slice out of the middle.
selector_t::value_type length_buf2[] = {3, 3};
selector_t::value_type stride_buf2[] = {3, 1};
selector_t length_val2(length_buf2, 2);
selector_t stride_val2(stride_buf2, 2);
std::cout &lt;&lt; "vi[gslice(9,{3,3},{3,1})]\n\n"
&lt;&lt; vi[std::gslice(9,length_val2,stride_val2)]
&lt;&lt; "\n\n";
// Print another two dimensional slice out of the middle but
// orthogonal to one we just did.
stride_val2[0] = 9;
stride_val2[1] = 1;
std::cout &lt;&lt; "vi[gslice(3,{3,3},{9,1})]\n\n"
&lt;&lt; vi[std::gslice(3,length_val2,stride_val2)]
&lt;&lt; "\n\n";
// Print out the last plane in the middle -- orthogonal to
// both of the previous ones.
stride_val2[0] = 3;
stride_val2[1] = 9;
std::cout &lt;&lt; "vi[gslice(1,{3,3},{3,9})]\n\n"
&lt;&lt; vi[std::gslice(1,length_val2,stride_val2)]
&lt;&lt; "\n\n";
// Now how about a diagonal slice, upper left front to lower right
// back.
stride_val2[0] = 3;
stride_val2[1] = 10;
std::cout &lt;&lt; "vi[gslice(0,{3,3},{3,10})]\n\n"
&lt;&lt; vi[std::gslice(0,length_val2,stride_val2)]
&lt;&lt; "\n\n";
return 0;
}
Program Output:
original valarray vi
[0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,
23,24,25,26]
vi[gslice(0,{3,3,3},{9,3,1})]
[0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,
23,24,25,26]
vi[gslice(9,{3,3},{3,1})]
[9,10,11,12,13,14,15,16,17]
vi[gslice(3,{3,3},{9,1})]
[3,4,5,12,13,14,21,22,23]
vi[gslice(1,{3,3},{3,9})]
[1,10,19,4,13,22,7,16,25]
vi[gslice(0,{3,3},{3,10})]
[0,10,20,3,13,23,6,16,26]
</PRE></UL>
<UL><PRE></PRE></UL>
<A NAME="sec9"><H3>See Also</H3></A>
<P><B><I><A HREF="valarray.html">valarray</A></I></B>, <B><I><A HREF="slice-array.html">slice_array</A></I></B>, <B><I><A HREF="slice.html">slice</A></I></B>, <B><I><A HREF="gslice-array.html">gslice_array</A></I></B>, <B><I><A HREF="mask-array.html">mask_array</A></I></B>, <B><I><A HREF="indirect-array.html">indirect_array</A></I></B></P>
<A NAME="sec10"><H3>Standards Conformance</H3></A>
<P><I>ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 26.3.6</I></P>
<BR>
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