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INFO: STL Sample for the inner_product Function

Article ID:157392
Last Review:September 23, 2003
Revision:3.0
This article was previously published under Q157392
NOTE: Microsoft Visual C++ NET (2002) supported both the managed code model that is provided by the .NET Framework and the unmanaged native Windows code model. The information in this article applies to unmanaged Visual C++ code only.
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SUMMARY

The sample code below illustrates how to use the inner_product STL function in Visual C++.

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MORE INFORMATION

Required Header

   #include <numeric>
   #include <functional>
				

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Prototype

   template<class InputIterator1, class InputIterator2, class _TYPE>

       inline _TYPE inner_product(InputIterator first, InputIterator last,
                           InputIterator first2, _TYPE init)

   template<class InputIterator1, class InputIterator2, class _TYPE,

            class BinaryOperator1, class BinaryOperator2> inline
       _TYPE inner_product(InputIterator1 first, InputIterator1 last,
                           InputIterator2 first2, _TYPE init,
                           BinaryOperator1 binary_op1,
                           BinaryOperator2 binary_op2)
				
NOTE: The class/parameter names in the prototype may not match the version in the header file. Some have been modified to improve readability.

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Description

inner_product computes its result by initializing the accumulator acc with init and then modifying it with:
acc = acc + (*i1) * (*i2)


- or -


acc = binary_op1(acc, binary_op2(*i1, *i2))
for every iterator i1 in the range [first, last) and iterator i2 in the range [first2, first2 + (last - first)) in order.

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Sample Code

/////////////////////////////////////////////////////////////////////// 
// 
// Compile options needed: /GX
// 
// inner_product.cpp : Demonstrates the use of inner_product().
// 
// Description of
//         inner_product(first,last,first2,init)
//         inner_product(first,last,first2,init,binary_op1,binary_op2):
// 
//    Computes its result by initializing the accumulator acc with init
//        acc = init
//    and then modifying it with
//        acc = acc  +  (*i1) * (*i2)
//    or
//        acc = binary_op1(acc, binary_op2(*i1, *i2))
//    for every iterator i1 in the range [first, last) and
//    iterator  i2  in  the  range [first2, first2 + (last - first))
//    in order.
// 
// Written by Shaun Miller
//  of Microsoft Product Support Services, Languages Developer Support.
// Copyright (c) 1996 Microsoft Corporation. All rights reserved.
/////////////////////////////////////////////////////////////////////// 

#include <iostream>
#include <numeric>
#include <functional>
#include <vector>
#include <iterator>

#if _MSC_VER > 1020   // if VC++ version is > 4.2
   using namespace std;  // std c++ libs implemented in std
   #endif

typedef vector < float, allocator < float > > FloatArray;
typedef ostream_iterator < float, char, char_traits<char> >
FloatOstreamIt;

void main ()

{

    FloatOstreamIt itOstream(cout," ");

    // Initialize the arrays
    FloatArray rgF1, rgF2;
    for (int i=1; i<=5; i++) {
        rgF1.push_back((float)i);
        rgF2.push_back((float)i*i);
    };

    // Print the arrays
    cout << "Array 1: ";
    copy(rgF1.begin(),rgF1.end(),itOstream);
    cout << endl;
    cout << "Array 2: ";
    copy(rgF2.begin(),rgF2.end(),itOstream);
    cout << endl;

    // Compute the inner_product of the arrays
    // This is the sum of the products (S.O.P) of the correspondingelements

    float ip1 = inner_product(rgF1.begin(),rgF1.end(),rgF2.begin(),0.0f);
    cout << "The inner product (S.O.P) of Array1 and Array2 is "
       << ip1
       << endl;

    // Compute the inner_product of the arrays
    // This is the product of the sums (P.O.S.) of the corresponding elements

    float ip2 = inner_product(rgF1.begin(),rgF1.end(),rgF2.begin(),1.0f,
                            multiplies<float>(),plus<float>());
    cout << "The inner product (P.O.S.) of Array1 and Array2 is "
       << ip2
       << endl;

} 
				
Program Output is:
Array 1: 1 2 3 4 5
Array 2: 1 4 9 16 25
The inner product (S.O.P) of Array1 and Array2 is 225
The inner product (P.O.S.) of Array1 and Array2 is 86400
				

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REFERENCES

Visual C++ Books On Line: Visual C++ Books:C/C++:Standard C++ Library Reference.

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APPLIES TO
The Standard C++ Library, when used with:
  Microsoft Visual C++ 4.2 Enterprise Edition
  Microsoft Visual C++ 5.0 Enterprise Edition
  Microsoft Visual C++ 6.0 Enterprise Edition
  Microsoft Visual C++ 4.2 Professional Edition
  Microsoft Visual C++ 5.0 Professional Edition
  Microsoft Visual C++ 6.0 Professional Edition
  Microsoft Visual C++ 6.0 Standard Edition
Microsoft Visual C++ .NET 2002 Standard Edition
Microsoft Visual C++ .NET 2003 Standard Edition

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Keywords: 
kbinfo kbcode KB157392

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