gslice(3C++)

Standard C++ Library
Copyright 1998, Rogue Wave Software, Inc.

NAME

gslice

- A numeric array class used to represent a generalized slice from an array.

SYNOPSIS

#include <valarray>
class gslice ;

DESCRIPTION

gslice_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 valarray. The gslice maps a set of n indices (ij), where n is equal to the number of strides, to a single index k.

When applied to a valarray using the gslice subscript operator (see valarray) a gslice produces a gslice_array. The gslice_array class creates a view into the original valarray that is tailored to match parameters of the gslice. The elements in a gslice_array are references to the elements in the original array.

INTERFACE

class gslice {
public:

// constructors

gslice();
gslice(size_t, const valarray<size_t>&,

const valarray<size_t>&);

gslice (const gslice&);

// Accessors

size_t start() const;
valarray<size_t> size() const;
valarray<size_t> stride() const;

};

CONSTRUCTORS

gslice();

Default constructor creates a gslice specifying no elements.

gslice(size_t start, const valarray<size_t>& length,

const valarray<size_t>& stride);

Creates a slice with starting index, length and stride as indicated by the arguments.

gslice(const gslice&)

Creates a slice with starting index, length and stride as indicated by the slice argument.

ACCESSORS

size_t start();

Returns the starting index of the gslice.

valarraysize_t> size();

Returns a valarray<size_t> containing the lengths of the gslice.

Valarray<size_t> stride();

Returns a valarray<size_t> containing the strides of the gslice.

EXAMPLE

//
// gslice.cpp
//
#include "valarray.h" // Contains a valarray stream inserter
using namespace std;

int main(void)
{

int ibuf[27] =

{0,1,2,3,4,5,6,7,8,1,2,3,4,5,6,7,8,9,2,3,4,5,6,7,8,9,10};

size_t len_buf[3] = {3,3,3};
size_t stride_buf[3] = {9,3,1};

// create a valarray of ints

valarray<int> vi(ibuf,27);

// create length and stride valarrays

valarray<size_t> len(len_buf,3);
valarray<size_t> stride(stride_buf,3);

// print out the valarray

cout << vi << endl;

// Print out all three dimensions (the entire valarray)

cout << valarray<int>(vi[gslice(0,len,stride)]) << endl;

// Print a two dimensional slice out of the middle

valarray<size_t> len2(2);
len2[0] = 3;
len2[1] = 3;
valarray<size_t> stride2(2);
stride2[0] = 3;
stride2[1] = 1;
cout << valarray<int>(vi[gslice(9,len2,stride2)]) << endl;

// Print another two dimensional slice out of the middle
// but orthogonal to one we just did

stride2[0] = 9;
stride2[1] = 1;
cout << valarray<int>(vi[gslice(3,len2,stride2)]) << endl;

// Print out the last plane in the middle,
// (orthogonal to both of the previous ones)

stride2[0] = 3;
stride2[1] = 9;
cout << valarray<int>(vi[gslice(1,len2,stride2)]) << endl;

// Now how about a diagonal slice?
// upper left front to lower right back

stride2[0] = 3;
stride2[1] = 10;
cout << valarray<int>(vi[gslice(0,len2,stride2)]) << endl;

return 0;

}

Program Output

[0,1,2,3,4,5,6,7,8,1,2,3,4,5,6,7,8,9,2,3,4,5,6,7,8,9,10]
[0,1,2,3,4,5,6,7,8,1,2,3,4,5,6,7,8,9,2,3,4,5,6,7,8,9,10]
[1,2,3,4,5,6,7,8,9]
[3,4,5,4,5,6,5,6,7]
[1,2,3,4,5,6,7,8,9]
[0,2,4,3,5,7,6,8,10]

WARNINGS

If your compiler does not support namespaces, then you do not need the using declaration for std.

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