Microsoft KB Archive/158614

= How to define operator== to compare one vector of user-defined types to another in Visual C++ =

Article ID: 158614

Article Last Modified on 1/10/2006

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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++ 2005 Express Edition</li></ul>

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

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

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This article was previously published under Q158614

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Note Microsoft Visual C++ .NET 2002 and Microsoft Visual C++ .NET 2003 support both the managed code model that is provided by the Microsoft .NET Framework and the unmanaged native Microsoft Windows code model. The information in this article applies only to unmanaged Visual C++ code. Microsoft Visual C++ 2005 supports both the managed code model that is provided by the Microsoft .NET Framework and the unmanaged native Microsoft Windows code model.

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SUMMARY
The following sample code illustrates how to define operator== to compare one vector of user-defined types to another.

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Prototypes
template<class _TYPE, class _A> inline bool operator==(const vector<_TYPE, _A>& _X,                  const vector<_TYPE, _A>& _Y); 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
The sample declares three empty vectors, of a user-defined class called ID, that each contain a Name string member and a Score integer member. It creates three vectors of IDs, then compares vectors using the operator== as defined for ID.

Sample Code
////////////////////////////////////////////////////////////////////// // // Compile options needed: /GX // //   Opequal.cpp : Illustrates how to define the operator== to compare //                 vectors. // // Functions: // //   vector::operator== - Vector equality comparison. //   vector::push_back - Appends (inserts) an element to the end of a //                        vector, allocating memory for it if necessary. // // Written by Tom Campbell // of Microsoft Corporation // Copyright (c) 1996 Microsoft Corporation. All rights reserved. //////////////////////////////////////////////////////////////////////

// The debugger can't handle symbols more than 255 characters long. // STL often creates symbols longer than that. // When symbols are longer than 255 characters, the warning is disabled.
 * 1) pragma warning(disable:4786)
 * 2) include
 * 3) include
 * 4) include
 * 5) include

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

// The ID class is used for team scoring. It holds each player's name // and score. class ID { public: string Name; int Score; ID : Name(""), Score(0) {} ID(string NewName, int NewScore) : Name(NewName), Score(NewScore) {} }; // In this example, an ID is equivalent only if both name and score match. bool operator==(const ID& x, const ID& y) { return (x.Name == y.Name) && (x.Score == y.Score); } // Define a template class for a vector of IDs. typedef vector<ID, allocator<ID> > NAMEVECTOR; void main {   // Declare 3 dynamically allocated vectors of names. NAMEVECTOR Vector1, Vector2, Vector3; // Create 3 short vectors of names. Vector1.push_back(ID("Karen Palmer", 2)); Vector1.push_back(ID("Ada Campbell", 1)); Vector2.push_back(ID("John Woloschuk", 3)); Vector2.push_back(ID("Grady Leno", 2)); Vector3.push_back(ID("Karen Palmer", 2)); Vector3.push_back(ID("Ada Campbell", 1)); // Compare Vector1 to Vector2 and show whether they're equivalent. Vector1 == Vector2 ? cout << "Vector1 == Vector2" : cout << "Vector1 != Vector2"; cout << endl; // Compare Vector1 to Vector3 and show whether they're equivalent. Vector1 == Vector3 ? cout << "Vector1 == Vector3" : cout << "Vector1 != Vector3"; cout << endl; }

Program Output
Vector1 != Vector2 Vector1 == Vector3

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