vector::operator<
Illustrates how to use the vector::operator< Standard Template Library (STL) function in Visual C++.
template<class _TYPE, class _A> inline
bool operator<(
const vector<_TYPE, _A>& _X,
const vector<_TYPE, _A>& _Y
);
Remarks
Note
The class/parameter names in the prototype do not match the version in the header file. Some have been modified to improve readability.
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.)
Example
// Opless.cpp
// compile with: /EHsc
// 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;
int 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));
cout << "Players and scores:" << endl;
for (theIterator = theVector.begin(); theIterator != theVector.end();
theIterator++)
cout << theIterator->Score << " "
<< theIterator->Name << endl;
cout << endl;
// Sort the vector of players by score.
sort(theVector.begin(), theVector.end());
// 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 << " "
<< theIterator->Name << endl;
}
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
Requirements
Header: <vector>