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Just started C++: Undefined Symbol error on Compile

Answer 1

+13 A:

It's complaining about main being undefined, and it's right. C and C++ require a standalone function named main which returns int. It is not sufficient to have a class with a method named main; the compiler only cares about the standalone one.

Another thing to remember is that the default visibility for members in a class type is private. Either change your class to use struct — that's pretty much the only difference between the two — or specify public visibility:

class Race {
public:
  void main() { ... }
};

Then you can call the main function from your class:

int main() {
  Race race;
  race.main();
  return EXIT_SUCCESS;
}

Rob Kennedy 2009-02-08 23:39:05

Nice catch on the default access level.

Bernard 2009-02-08 23:44:15

Answer 2

+3 A:

You need a main() function to give the program a starting point:

int main()
{
     // whatever...
     // Maybe:

     Race race;

     race.main();
}

But it would probably make sense to have many of your methods be static methods since they don't rely on any instance members of the Race class.

Michael Burr 2009-02-08 23:39:30

If you're going to use static methods, I would tend to just use functions. Perhaps in a namespace.

Bernard 2009-02-08 23:44:55

You'll get no argument from me.

Michael Burr 2009-02-09 00:55:26

Answer 3

+3 A:

You need a main function:

// The arguments are only needed if passing arguments to your program.
// You could just use `int main()`.
int main(int argc, char** argv)
{
    Race race;
    race.executeRace();
}

or so, without seeing your specific error.

Bernard 2009-02-08 23:41:04

Answer 4

+3 A:

C++ is really nothing like Java. For example, functions don't have to be part of a class. You need to move the function main() so that it is outside the class.

class Race {
  // stuff
};

int main() {
  // stuff
}

anon 2009-02-08 23:41:19

Answer 5

+2 A:

Perhaps this is what you meant

#include <cstdlib>
#include <ctime>
#include <iostream>
#include <string>

using namespace std;



class Race
{

public:
    void ExecuteRace()
    {
        int rabbitPosition = 1;
        int turtlePosition = 1;

        cout << "BANG!!!" << endl << "AND THEY'RE OFF!!!";

        while (rabbitPosition <=70 && turtlePosition <=70)
        {
            printPositions(rabbitPosition, turtlePosition);

            turtlePosition = turtleMoveSquares(turtlePosition);
            rabbitPosition = rabbitMoveSquares(rabbitPosition);
        }

        printWinner(rabbitPosition, turtlePosition);

        tie(rabbitPosition, turtlePosition);
    }

private:
    int randomMove()
    {
        srand(time(NULL));
        int randomInt = rand() % 100 + 1;
        return randomInt;
    }


    int turtleMoveSquares(int tPosition)
    {

        int turtleMove = randomMove();

        if(turtleMove >=1 && turtleMove <= 40)
            tPosition = tPosition + 4;

        if(turtleMove >= 41 && turtleMove <= 50 )
            tPosition = tPosition - 2;

        if(turtleMove >=51 && turtleMove <=100)
            tPosition = tPosition + 2;

        if(tPosition < 1)
            tPosition = 1;

        return tPosition;
    }


    int rabbitMoveSquares(int rabbitPosition)
    {

        int rabbitMove = randomMove();

        if(rabbitMove >=1 && rabbitMove <= 25)
            rabbitPosition = rabbitPosition;

        if(rabbitMove >=26 && rabbitMove <= 55)
            rabbitPosition = rabbitPosition + 10;

        if(rabbitMove >=56 && rabbitMove <=60)
            rabbitPosition = rabbitPosition - 15;

        if(rabbitMove >=61 && rabbitMove <= 90)
            rabbitPosition = rabbitPosition + 5;

        if(rabbitMove >=90 && rabbitMove <=100)
            rabbitPosition = rabbitPosition - 3;

        if(rabbitPosition < 1)
            rabbitPosition = 1;

        return rabbitPosition;
    }

    void printPositions(int rabbitPositions, int turtlePositions)
    {
        int turtleCount;
        int rabbitCount;
        int endCount;

        if(rabbitPositions == turtlePositions && rabbitPositions != 1)
        {
            turtleCount = 1;

            while(turtleCount < turtlePositions)
            {
                cout << "-";
                turtleCount = turtleCount+1;
            }
            cout << "OUCH!";
        }

        else
        {
            turtleCount = 1;
            rabbitCount = 1;
            endCount=1;

            if(turtlePositions < rabbitPositions)
            {
                while(turtleCount < turtlePositions)
                {
                    cout <<  "-";
                    turtleCount = turtleCount+1;
                }

                cout << "T";

                while(rabbitCount < (rabbitPositions - turtlePositions))
                {
                    cout <<  "-";
                    rabbitCount = rabbitCount+1;
                }
                cout << "H";

            }

            if(rabbitPositions < turtlePositions)
            {
                while(rabbitCount < rabbitPositions)
                {
                    cout << "-";
                    rabbitCount = rabbitCount+1;
                }
                cout << "H";

                while(turtleCount < (turtlePositions - rabbitPositions))
                {
                    cout << "-";
                    turtleCount = turtleCount+1;
                }
                cout << "T";

                cout << "\n";
            }
        }
    }

    void printWinner(int rabbitPosition, int turtlePosition)
    {
        if(turtlePosition >= 70 && rabbitPosition < 70)
        {
            cout << "TORTOISE WINS!!! YAY!!!\n";
        }
        else if(rabbitPosition >=70 && turtlePosition < 70)
        {
            cout << "Hare wins. Yuch.\n";
        }
        else if(rabbitPosition >=70 && turtlePosition >=70)
        {
            cout << "It's a tie\n";
        }
    }

    void tie(int turtlePosition, int rabbitPosition)
    {
        if(rabbitPosition >=70 && turtlePosition >=70)
            ExecuteRace();
    }
};


void main()
{
    Race race;
    race.ExecuteRace();
}

SDX2000 2009-02-08 23:42:19

Function main always returns int, never void. People who use that as a shibboleth will judge you for it, and your program will have undefined behavior.

Rob Kennedy 2009-02-09 00:28:51

"People who use that as a shibboleth" hahaha good one. I am just using the same code as the OP so that he knows what goes where.

SDX2000 2009-02-09 07:34:49

Answer 6

+1 A:

You have no main function.

C++'s biggest difference from Java is that its main() function has this signature (parameters optional):

int main(int argc, char** argv);

And it is in the global namespace. This is the function invoked at program start, and probably why you're missing a symbol.

Try adding this to your program:

int main() {
    Race r;
    r.main();
    return 0;
}

Alternatively, you can do away with the class entirely since you're not actually doing anything with it.

greyfade 2009-02-08 23:42:39

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Just started C++: Undefined Symbol error on Compile

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