Vector Class, operator< (STL Sample)

The sample code below illustrates how to use the the vector class operator< STL function in Visual C++.

Required Header:
<vector>

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 do not match the version in the header file. Some have been modified to improve readability.

Description:
The sample declares an empty vector of IDs, a user-defined type. It initializes and adds four IDs to the vector in random order. It sorts them using the operator< defined for ID and generates the newly sorted vector. (Note that it sorts in order of Score, not Name.)

Sample Code:

//////////////////////////////////////////////////////////////////////
//
// Compile options needed: /GX
//
//    Opless.cpp -- Illustrates the defining the < operator to sort vectors
//
// Functions:
//
//    operator< - Vector comparison operator.
//
//    vector::begin - Returns an iterator to start traversal of the vector.
//
//    vector::end - Returns an iterator for the last element of the vector.
//
//    vector::iterator - Traverses the vector.
//
//    vector::push_back - Appends (inserts) an element to the end of a
//                        vector, allocating memory for it if necessary.
//
//    sort algorithm - Sorts the vector.
//
//////////////////////////////////////////////////////////////////////

// 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>

using namespace std ;

// 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);
}

// IDs will be sorted by Score, not by Name.
bool operator<(const ID& x, const ID& y)
{
    return x.Score < y.Score;
}

// Define a template class for a vector of IDs.
typedef vector<ID> NAMEVECTOR;

void main()
{
    // Declare a dynamically allocated vector of IDs.
    NAMEVECTOR theVector;

    // Iterator is used to loop through the vector.
    NAMEVECTOR::iterator theIterator;

    // Create a pseudo-random vector of players and scores.
    theVector.push_back(ID("Karen Palmer", 2));
    theVector.push_back(ID("Ada Campbell", 1));
    theVector.push_back(ID("John Woloschuk", 3));
    theVector.push_back(ID("Grady Leno", 2));

    for (theIterator = theVector.begin(); theIterator != theVector.end();
         theIterator++)
        cout << theIterator->Score  << "\t"
             << theIterator->Name << endl;
    cout << endl;

    // Sort the vector of players by score.
    sort(theVector.begin(), &theVector[theVector.size()]);

    // Output the contents of the vector in its new, sorted order.
    cout << "Players ranked by score:" << endl;
    for (theIterator = theVector.begin(); theIterator != theVector.end();
         theIterator++)
        cout << theIterator->Score  << "\t"
             << theIterator->Name << endl;
    cout << endl << endl;
}

Program Output is:

Players and scores:
2       Karen Palmer
1       Ada Campbell
3       John Woloschuk
2       Grady Leno

Players ranked by score:
1       Ada Campbell
2       Karen Palmer
2       Grady Leno
3       John Woloschuk