Microsoft KB Archive/157671

= INFO: STL Sample for the advance Function =

Article ID: 157671

Article Last Modified on 9/23/2003

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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</li></ul>

 Microsoft Visual C++ 5.0 Professional Edition</li></ul>

 Microsoft Visual C++ 6.0 Professional Edition</li></ul>

 Microsoft Visual C++ 6.0 Standard Edition</li></ul>

 Microsoft Visual C++ .NET 2002 Standard Edition</li></ul>

 Microsoft Visual C++ .NET 2003 Standard Edition</li></ul> </li></ul>

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This article was previously published under Q157671

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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 advance STL function in Visual C++.

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MORE INFORMATION
Because only random access iterators provide + and - operators, the library provides two template functions, advance and distance.

Prototype
template<class InIt, class Dist>

void advance(InIt& it, Dist n);

Description
The advance function accepts two parameters:
 * InIt: The iterator to advance.
 * Dist: The number of elements to increment the iterator by.

The advance function advances the iterator n times. If the iterator is a random-access iterator type, the function evaluates the expression as <pre class="fixed_text">  iterator += n. Otherwise, it performs each increment by evaluating: <pre class="fixed_text">  ++iterator. If the iterator is an input or forward iterator type, n must not be negative.

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

Sample Code
////////////////////////////////////////////////////////////////////// // // Compile options needed: /GX // // : Advance.cpp // // Functions: // //   advance // // Written by Linda Koontz // of Microsoft Product Support Services, // Copyright (c) 1996 Microsoft Corporation. All rights reserved. //////////////////////////////////////////////////////////////////////

/* Compile options needed: /GX
 * 1) include
 * 2) include
 * 3) include
 * 1) include

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


 * 1) pragma warning (disable:4786)

typedef list<string, allocator > STRLIST;

void main { STRLIST List; STRLIST::iterator iList; STRLIST::difference_type dTheDiff;

List.push_back("A1"); List.push_back("B2"); List.push_back("C3"); List.push_back("D4"); List.push_back("E5"); List.push_back("F6"); List.push_back("G7");

// Print out the list iList=List.begin; cout << "The list is: "; for (int i = 0; i < 7 ; i++, iList++) cout << *iList << "  ";

// Initialize to the first element"   iList=List.begin;    cout << "\n\nAdvance to the 3rd element." << endl;    advance(iList,2);    cout << "The element is " << *iList << endl;    dTheDiff = distance( List.begin, iList);

} Program Output is: <pre class="fixed_text">The list is: A1 B2  C3  D4  E5  F6  G7

Advance to the 3rd element.

The element is C3

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