Sort vector of pointers to objects

[ricardo46]

Im creating a program for a race. The Race class has a vector of results and each element of that vector is a pointer to a result. The Result class has a Time and a pointer to a Participant. So in each race there are various results and it is a result for each participant.
The Time is a class that has hours, minutes and seconds.
How can I sort the vector of results from the result of the participant with the fastest time to the result of the participant with the slowest time?
My code is like this:

//.h file:

  class Time
{
    unsigned int hours;
    unsigned int minutes;
    unsigned int seconds;
public:
    Time(unsigned int h, unsigned int m, unsigned int s, unsigned int ms);
    Time();
    unsigned int gethours();
    unsigned int getMinuts();
    unsigned int getSeconds();
    string show();
};

class Participant {
    string name;
    unsigned int age;
    string country;
public:
    Participant(string n, unsigned int a, string c);
    string getName();
    string getCountry();
    int getAge();
    string show() const;
};

class Result {
    Participant *part;
    Time time;
public:
    Result(Participant  *p, Time t);
    Participant *getParticipant() const;
    Time getTime();
    string show();
    bool isFastest(Result& *res1, Result& *res2) const;
};

class Race {
    string name;
    float distance;
    vector<Result *> results;
public:
    Race(string nm, float dist);
    string getName();
    float getDistance();
    void sortResults();
    void addResult(Result *r);
    string showRaceResults();
    string show();
};

//.cpp file:

//not sure if I should pass the pointers as reference and not sure if this function must be const

bool Result::isFastest(Result& *res1, Result& *res2) const{ 
    if (res1.getTime()->gethours() < res2.getTime()->gethours())
        return true;
    else {
        if (res1.getTime()->gethours() > res2.getTime()->gethours())
            return false;
        else {
            if (res1.getTime()->getMinutes() < res2.getTime()->getMinutes())
                return true;
            else {
                if (res1.getTime()->getMinutes()) > res2.getTime()->getMinutes())
                    return false;
                else {
                    if (res2.getTime()->getSeconds() < res2.getTime()->getSeconds())
                        return true;
                    else {
                            return false;
                        }
                }
            }
        }
    }
}

void Race::sortResults() {
    sort (results.begin(), results.end(), isFastest);
}

What am I missing to get my code to work?

[dhayden]

Use std::sort(). See the second variant here: http://www.cplusplus.com/reference/algorithm/sort/

In particular, note that you will need to write your own comparison function that drills down to the participant's and compares their times.

[cire]

If you want to pass a pointer by reference (although you don't need to here) you've got the syntax wrong:

bool isFaster(Result*& a, Result*& b)

But, as I said, that isn't necessary. Nor is it necessary for your comparison function to be a member of Result. Your comparison is a typical less-than comparison so the name should reflect that, isFastest does not.

After numerous changes to make your code const correct, the function might look like so:

bool isFaster(const Result* a, const Result* b)
{
    const Time aTime = a->getTime();
    const Time bTime = b->getTime();

    if (aTime.getHours() < bTime.getHours())
        return true;

    if (aTime.getMinutes() < bTime.getMinutes())
        return true;

    return aTime.getSeconds() < bTime.getSeconds();
}

void Race::sortResults() {
    sort(results.begin(), results.end(), isFaster);
}

[ricardo46]

Where exactly should I put the isFaster function? In the cpp, in the .h or in the main?
Im lost!

[cire]

The implementation would go in the cpp file. There isn't necessarily any reason to include a declaration/prototype in the .h file since it doesn't need to be visible to code using the class interface.

[dhayden]

I think cire's isFaster() may not be quite right. For example, if aTime is 10:11:12 and bTime is 12:20:21, it will think that aTime < bTime. The right code is more like:

bool isFaster(const Result* a, const Result* b)
{
    const Time aTime = a->getTime();
    const Time bTime = b->getTime();

    if (aTime.getHours() < bTime.getHours())
        return true;
    if (aTime.getHours() > bTime.getHours())
        return false;

    // hours are equal.
    if (aTime.getMinutes() < bTime.getMinutes())
        return true;
    if (aTime.getMinutes() > bTime.getMinutes())
        return false;

    // Minutes are equal
    return aTime.getSeconds() < bTime.getSeconds();
}

[cire]

I think cire's isFaster() may not be quite right.

I think you're right. Thanks for the correction.

[ricardo46]

Thank you very much for your help.
I put the isFaster function in the .cpp file but I get two errors:

First in both this lines:
const Time aTime = a->getTime();
const Time bTime = b->getTime();
I get this error:
Multiple markers at this line
- Invalid arguments ' Candidates are: Time getTime() '
- passing 'const Result' as 'this' argument of 'Time Result::getTime()' discards qualifiers [- fpermissive]


Then in every line that has an if i get:
Multiple markers at this line
- Invalid arguments ' Candidates are: unsigned int getHoras() '
- Invalid arguments ' Candidates are: unsigned int getHoras() '
- passing 'const Tempo' as 'this' argument of 'unsigned int Tempo::getHoras()' discards
qualifiers [-fpermissive]

[dhayden]

The problem is that *a and *b are const, but you're calling the non-const functions a->getTime(). Declare & define Result::getTime() to be const.

You will also need to declare/define the gethours, getMinutes and getSeconds methods of Time as const:

    unsigned int gethours() const;
    unsigned int getMinuts() const;
    unsigned int getSeconds() const;

[ricardo46]

Yes that solved all the problems!
Thank you very much!