indirect_array Class

 

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

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.

// 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).  

Header: <valarray>

Namespace: std

Thread Safety in the C++ Standard Library

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