Module: Standard C++ Library Library: Numerics
Does not inherit
|
mask_array() operator%=() operator&=() |
operator>>=() operator<<=() operator*=() |
operator+=() operator-=() operator/=() |
operator=() operator^=() operator| |
A numeric array class that gives a masked view of a valarray
#include <valarray>
namespace std {
template <class T>
class mask_array;
}
mask_array gives a masked view into a valarray. A mask_array can only be produced by applying the mask subscript operator to a valarray. This subscript operator takes a valarray<bool> argument and produces a mask_array. Only the elements in the valarray whose corresponding elements in the valarray<bool> argument were true are selected by the mask_array. The elements in a mask_array are references to selected elements in the valarray (so changing an element in the mask_array really changes the corresponding element in the valarray). A mask_array does not itself hold any distinct elements. The template cannot be instantiated directly since all its constructors are private. However, you can copy a mask_array to a valarray using either the valarray copy constructor or the assignment operator. Reference semantics are lost at that point.
namespace std {
template <class T> class mask_array {
public:
// types
typedef T value_type;
// destructor
~mask_array();
// public assignment
void operator=(const valarray<T>& array) const;
// computed assignment
void operator*=(const valarray<T>& array) const;
void operator/=(const valarray<T>& array) const;
void operator%=(const valarray<T>& array) const;
void operator+=(const valarray<T>& array) const;
void operator-=(const valarray<T>& array) const;
void operator^=(const valarray<T>& array) const;
void operator&=(const valarray<T>& array) const;
void operator|=(const valarray<T>& array) const;
void operator<<=(const valarray<T>& array) const;
void operator>>=(const valarray<T>& array) const;
// other
void operator=(const T&) const;
private:
// constructors
mask_array();
mask_array(const mask_array<T>&);
// operator=
mask_array<T>& operator=(const mask_array<T>& array);
};
}
mask_array(); mask_array(const mask_array&);
All mask_array constructors are private and cannot be called directly. This prevents copy construction of mask_arrays.
void operator=(const valarray<T>& x) const;
Assigns values from x to the selected elements of the valarray that self refers to. Remember that a mask_array never holds any elements itself, it simply refers to selected elements in the valarray used to generate it.
mask_array<T>& operator=(const mask_array<T>& x);
Private assignment operator. Cannot be called directly, thus preventing assignment between mask_arrays.
void operator*=(const valarray<T>& val) const; void operator/=(const valarray<T>& val) const; void operator%=(const valarray<T>& val) const; void operator+=(const valarray<T>& val) const; void operator-=(const valarray<T>& val) const; void operator^=(const valarray<T>& val) const; void operator&=(const valarray<T>& val) const; void operator|=(const valarray<T>& val) const; void operator<<=(const valarray<T>& val) const; void operator>>=(const valarray<T>& val) const;
Applies the indicated operation using elements from val to the selected elements of the valarray that self refers to. Remember that a mask_array never holds any elements itself; it simply refers to selected elements in the valarray used to generate it.
void operator=(const T& x) const;
Assigns x to the selected elements of the valarray that self refers to.
//
// mask_array.cpp
//
#include <valarray.h> // Includes valarray and
// provides stream inserter.
typedef std::valarray<int> valarray_t;
typedef std::valarray<bool> maskarray_t;
int main(void) {
// Create a valarray of ints.
valarray_t::value_type ibuf[10] = {0,1,2,3,4,5,6,7,8,9};
valarray_t vi(ibuf, 10);
// Create a valarray of bools for a mask.
maskarray_t::value_type mbuf[10] = {1,0,1,1,1,0,0,1,1,0};
maskarray_t mask(mbuf,10);
// Print out the valarray<int>.
std::cout << "original valarray<int> vi\n\n" << vi << "\n\n";
// Print out the valarray<bool>.
std::cout << "original valarray<bool> mask\n\n" << mask
<< "\n\n";
// Print a mask array.
std::cout << "vi[mask]\n\n" << vi[mask] << "\n\n";
// Double the values of the masked array and print out.
vi[mask] += static_cast<valarray_t> (vi[mask]);
std::cout << "vi[mask] += vi[mask]\n\n" << vi << std::endl;
return 0;
}
Program Output:
original valarray<int> vi [0,1,2,3,4,5,6,7,8,9] original valarray<bool> mask [1,0,1,1,1,0,0,1,1,0] vi[mask] [0,2,3,4,7,8] vi[mask] += vi[mask] [0,1,4,6,8,5,6,14,16,9]
slice, slice_array, valarray, gslice, gslice_array, indirect_array
ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 26.3.8
Copyright (c) 1994-2006 Rogue Wave Software, a Quovadx Division.
Licensed under the Apache License, Version 2.0.
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