indirect_array class

An internal, auxiliary class template that supports objects that are subsets of valarray objects by providing operations between subset arrays defined by specifying a subset of indices of a parent valarray.

Syntax

Remarks

The class describes an object that stores a reference to an object va of class valarray<Type>, along with an object xa of class valarray<size_t>, which describes the sequence of elements to select from the valarray<Type> object.

You construct an indirect_array<Type> object only by writing an expression of the form va[xa]. The member functions of class indirect_array then behave like the corresponding function signatures defined for valarray<Type>, except that only the sequence of selected elements is affected.

The sequence consists of xa.size elements, where element I becomes the index xa[I] within va.

Example:

// indirect_array.cpp
// compile with: /EHsc
#include <valarray>
#include <iostream>

int main( )
{
   using namespace std;
   int i;

   valarray<int> va ( 10 );
   for ( i = 0 ; i < 10 ; i += 2 )
      va [ i ] =  i;
   for ( i = 1 ; i < 10 ; i += 2 )
      va [ i ] =  -1;

   cout << "The initial operand valarray is:  ( ";
      for ( i = 0 ; i < 10 ; i++ )
         cout << va [ i ] << " ";
   cout << ")." << endl;

   // Select 2nd, 4th & 6th elements
   // and assign a value of 10 to them
   valarray<size_t> indx ( 3 );
   indx [0] = 2;
   indx [1] = 4;
   indx [2] = 6;
   va[indx] = 10;

   cout << "The modified operand valarray is:  ( ";
      for (i = 0 ; i < 10 ; i++ )
         cout << va [ i ] << " ";
   cout << ")." << endl;
}

Output

The initial operand valarray is:  (0 -1 2 -1 4 -1 6 -1 8 -1).
The modified operand valarray is:  (0 -1 10 -1 10 -1 10 -1 8 -1).

Requirements

Header: <valarray>

Namespace: std

See also

Thread safety in the C++ Standard Library