STL Sample for the Vector Class Using the operator== Function

ID: Q158614

The information in this article applies to:

The Standard C++ Library, included with:
- Microsoft Visual C++, 32-bit Editions, version 4.2

SUMMARY

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

MORE INFORMATION

Required Headers


   <vector>
   <algorithm>

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.
#pragma warning(disable:4786)
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>

// 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

REFERENCES

Visual C++ Books Online: Visual C++ Books; C/C++; Standard C++ Library Reference

Additional query words: STL STLSample


Keywords          : kbcode STLIss 
Version           : WINNT:4.2;
Platform          : NT WINDOWS 
Issue type        : kbhowto

Last Reviewed: July 22, 1999