mask_array(3C++) - mask_array(3C++)
Standard C++ Library Copyright 1998, Rogue Wave Software, Inc.
NAMEmask_array
- A numeric array class that gives a masked view of a valarray.
SYNOPSIS
#include <valarray>
template <;class T>
class mask_array;
DESCRIPTION
mask_array<T> gives a masked view into a valarray. mask_arrays are only
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 ele‐
ments 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 slice_array to a valarray using either the valarray copy
constructor or the assignment operator. Reference semantics are lost at
that point.
INTERFACE
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);
};
CONSTRUCTORSmask_array();
mask_array(const mask_array&);
All mask_array constructors are private and cannot be called directly. This
prevents copy construction of mask_arrays.
ASSIGNMENT OPERATORS
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.
COMPUTED ASSIGNMENT OPERATORS
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.
MEMBER FUNCTIONS
void operator= (const T& x) const;
Assigns x to the selected elements of the valarray that self refers to.
EXAMPLE
//
// mask_array.cpp
//
#include "valarray.h" // Contains a valarray stream inserter
using namespace std;
int main(void)
{
int ibuf[10] = {0,1,2,3,4,5,6,7,8,9};
bool mbuf[10] = {1,0,1,1,1,0,0,1,1,0};
// create a valarray of ints
valarray<int> vi(ibuf,10);
// create a valarray of bools for a mask
valarray<bool> mask(mbuf,10);
// print out the valarray<int>
cout << vi << endl;
// Get a mask array and assign that mask to another array
mask_array<int> msk = vi[mask];
valarray<int> vi3 = msk;
// print out the masked_array
cout << vi3 << endl;
// Double the masked values
msk += vi3;
// print out vi1 again
cout << vi << endl;
return 0;
}
Program Output
[0,1,2,3,4,5,6,7,8,9]
[0,2,3,4,7,8]
[0,1,4,6,8,5,6,14,16,9]
WARNINGS
If your compiler does not support namespaces, then you do not need the
using declaration for std.
SEE ALSO
slice, slice_array, valarray, gslice, gslice_array, indirect_array
Rogue Wave Software 02 Apr 1998 mask_array(3C++)
