Microsoft KB Archive/157220

Knowledge Base

How to use the exp, log, and log10 STL functions in Visual C++

Article ID: 157220

Article Last Modified on 12/30/2005

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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 2003 Standard Edition
  • Microsoft Visual C++ .NET 2002 Standard Edition
  • Microsoft Visual C++ 2005 Express Edition

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This article was previously published under Q157220

SUMMARY

The sample code below illustrates how to use the exp, log, and log10 STL functions in Visual C++.

MORE INFORMATION

Required Header

   <valarray>
   <math>
                

Prototype

   / exp
   template<class T>
   valarray<T> exp(const valarray<T>& x);

   // log
   template<class T>
   valarray<T> log(const valarray<T>& x);

   // log10
   template<class T>
   valarray<T> log10(const valarray<T>& x);
                

NOTE: The class/parameter names in the prototype may not match the version in the header file. Some have been modified to improve readability.

Description

This article illustrates the use of STL exp(), log(), and log10() functions through sample code.

Sample Code

////////////////////////////////////////////////////////////////////// 
// 
// Compile options needed: None
// 
// <filename> :  main.cpp
// 
// Functions:
// 
//    exp, log, log10
// 
// Written by Yeong-Kah Tam
// of Microsoft Product Support Services,
// Copyright (c) 1996 Microsoft Corporation. All rights reserved.
////////////////////////////////////////////////////////////////////// 

// disable warning C4267: possible loss of data,
// okay to ignore

#pragma warning(disable: 4267)

#include <iostream>                 // for i/o functions
#include <valarray>                 // for valarray
#include <math.h>                   // for exp(), log(), and log10()

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

#define ARRAY_SIZE  3               // array size

typedef valarray<double> DB_VARRAY;
void main()

{
    int i;
    // Set val_array to contain values 1, 10, 100 for the following test.
    DB_VARRAY val_array(ARRAY_SIZE);
    for (int i = 0; i < ARRAY_SIZE; i++)
        val_array[i] = pow(10.0, i);

    // Display the size of val_array.
    cout << "Size of val_array = " << val_array.size() << "\r\n";

    // Display the content of val_array before calling exp, log, and
    // log10 functions.
    cout << "The values in val_array:\r\n";
    for (i = 0; i < ARRAY_SIZE; i++)
        cout << val_array[i] << "    ";
    cout << "\r\n\r\n";

    // rvalue_array to hold the return value from calling the sqrt() and
    // pow() functions.
    DB_VARRAY rvalue_array;

    // ----------------------------------------------------------------
    // exp() - display the content of rvalue_array
    // ----------------------------------------------------------------
    rvalue_array = exp(val_array);
    cout << "The result after calling exp():\r\n";
    for (i = 0; i < ARRAY_SIZE; i++)
        cout << rvalue_array[i] << "     ";
    cout << "\r\n\r\n";

    // ----------------------------------------------------------------
    // log() - display the content of rvalue_array
    // ----------------------------------------------------------------
    rvalue_array = log(val_array);
    cout << "The result after calling log():\r\n";
    for (i = 0; i < ARRAY_SIZE; i++)
        cout << rvalue_array[i] << "     ";
    cout << "\r\n\r\n";

    // ----------------------------------------------------------------
    // log10() - display the content of rvalue_array
    // ----------------------------------------------------------------
    rvalue_array = log10(val_array);
    cout << "The result after calling log10():\r\n";
    for (i = 0; i < ARRAY_SIZE; i++)
        cout << rvalue_array[i] << "     ";
    cout << "\r\n\r\n";

}
                

Output:

Size of val_array = 3

The values in val_array:

1    10    100

The result after calling exp():

2.71828     22026.5     2.68812e+043

The result after calling log():
0     2.30259     4.60517

The result after calling log10():

0     1     2
                

Note For more information about the pow function in Visual C++ 2005, visit the following Microsoft Developer Network (MSDN) Web site:

http://msdn2.microsoft.com/en-us/library/e2b159c0.aspx

REFERENCES

For more information about exp, log, and log10, visit the following MSDN Web site:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vcstdlib/html/vcsampsampleexplogandlog10sample.asp

Additional query words: STL STLSample exp log log10

Keywords: kbhowto kbinfo kbcode KB157220

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