From Forum Nokia Wiki

ID	CS001099	Creation date	September 16, 2008
Platform	S60 3rd Edition, FP2	Tested on devices	Nokia 6220 Classic
Category	Open C/C++	Subcategory	Files/Data

Keywords (APIs, classes, methods, functions): vector, sort()

Overview

This code snippet shows how to use C++ Standard Template Library (STL) sort function with user-defined new types using structs or classes. The sort function needs at least two parameters: start and end. These iterator parameters are used to sort the range of elements between them. An optional third parameter has the default less-than operator as a value to compare elements.

None of the comparison operators are defined in the user-defined classes by default, so the sort function is not able to compare two objects until the less-than operator is overloaded. Assignment between classes or structs also needs user-defined implementation if dynamic allocation is used with member variables.

Note: In order to use this code, you need to install the Open C/C++ plug-in.

This snippet can be self-signed.

MMP file

The following libraries are required:

LIBRARY  libstdcpp.lib
LIBRARY  libc.lib
LIBRARY  euser.lib

Source file

#include <iostream>
#include <algorithm>
#include <list>
#include <vector>
#include <string>
 
using namespace std;
 
// SCORE STRUCT
struct Score
{  
  int val1;
  int val2;
  bool operator==(const Score& score) const;
  bool operator<(const Score& score) const;
};
 
bool Score::operator==(const Score& score) const
{
  return(score.val1 == val1 &&
       score.val2 == val2);
}
 
bool Score::operator<(const Score& score) const
{
  if(val2 < score.val2)
    return true;      
  else if (val2 == score.val2 && val1 < score.val1)
    return true;
  else return false;
}
 
//user defined compare function that compares only val1 variables
bool exampleCompare( Score s1, Score s2 ) 
{
  return s1.val1 < s2.val1;
};
 
 
// SCORE CLASS
class ScoreClass
{
public:
  friend ostream& operator<<(ostream& output, const ScoreClass& c);
  ScoreClass(string s, int v1, int v2);  
  bool operator==(const ScoreClass& score) const;
  bool operator<(const ScoreClass& score) const;
  string getStr() const;
private:
  string str;
  int val1;
  int val2;
};
 
ostream& operator<<(ostream& output, const ScoreClass& c) 
{
    output   << c.str << ' ' << c.val1 << ' ' << c.val2;
    return output;  
}
ScoreClass::ScoreClass(string s, int v1, int v2)
{
  str = s; val1 = v1; val2 = v2;
}
 
bool ScoreClass::operator==(const ScoreClass& score) const
{
  return(score.str == str &&         
       score.val1 == val1 &&
       score.val2 == val2);
}
 
bool ScoreClass::operator<(const ScoreClass& score) const
{
  if(val2 < score.val2)
    return true;      
  else if (val2 == score.val2 && val1 < score.val1)
    return true;
  else return false;
}
string ScoreClass::getStr() const
{
  return str;
}
 
 
//user defined compare function that compares string values
bool exampleCompare2(ScoreClass s1, ScoreClass s2) 
{
  return (s1.getStr() < s2.getStr());
}
 
 
int main()
{
  int vectorElements = 0;
 
//-- Sorting struct types --
  
  vector<Score> structVector;
  Score first = {3, 2};
  Score second = {1, 5};
  Score third = {2, 3};
  
  structVector.push_back(first);
  structVector.push_back(second);
  structVector.push_back(third);
 
  vectorElements = structVector.size();
  
  sort(structVector.begin(), structVector.end());
  
   for (int i=0; i<vectorElements; ++i) //3 2|2 3|1 5|
     {
     cout << structVector[i].val1 << ' '
          << structVector[i].val2 << '|';
     }
 
   //use function exampleCompare to sort list again
  sort(structVector.begin(), structVector.end(), exampleCompare);
   
  for (int i=0; i<vectorElements; ++i) //1 5|2 3|3 2|
      {
      cout << structVector[i].val1 << ' '
           << structVector[i].val2 << '|';
      }
   
//-- Sorting class types --
 
  vector<ScoreClass> classVector;
  classVector.push_back(ScoreClass((string)"111", 10, 20));
  classVector.push_back(ScoreClass((string)"222", 60, 200));
  classVector.push_back(ScoreClass((string)"333", 1, 1));
  vectorElements = classVector.size();
 
  sort(classVector.begin(), classVector.end()); //333 1 1|111 10 20|222 60 200|
 
  for (int i=0; i<vectorElements; ++i) 
    {
   cout << classVector[i] << '|';
  }
  
  //use function exampleCompare2 to sort list again
  sort(classVector.begin(), classVector.end(), 
    exampleCompare2); //111 10 20|222 60 200|333 1 1| 
 
  for (int i=0; i<vectorElements; ++i) 
    {
    cout << classVector[i] << '|';
    }
 
  return 0;
}

Postconditions

The STL sort function is used to sort vectors that contain structs and classes and the sorted contents are displayed on the screen.

See also

CS001098 - Sorting predefined types using STL sort