c++ - 刚开始 C++ : Undefined Symbol error on Compile

Question

情况是这样的:

我刚刚开始我的第一门 C++ 类(class)。我对 C++ 一无所知，尽管这是 C++ 类(class)的介绍，但老师几乎没有教授该语言的语法，只是我们已经知道的逻辑。

现在他给了我们一个程序描述，然后说:“写吧，哈哈。”我理解逻辑很好，但正如我之前所说，我对 C++ 一无所知。因此，我首先用 java 编写它(我确实知道)，然后一旦我用 java 编写它，我就尝试将它编码为 C++。

但是现在编译时出现以下错误

uxb3% g++ -o Race race.cc
Undefined                       first referenced
 symbol                             in file
main                                /usr/local/gcc-4.1.1/bin/../lib/gcc/sparc-sun-solaris2.10/4.1.1/crt1.o
ld: fatal: Symbol referencing errors. No output written to Race
collect2: ld returned 1 exit status

有人可以帮我解决这个问题吗？

这是我在 .txt 文件中的代码: http://rapidshare.com/files/195742284/race.txt.html

这里是复制粘贴:

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

using namespace std;
class Race
{

        void main()
        {
                executeRace();
        }

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

        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);
        }

        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();
        }
};

Answer 1

它提示 main 未定义，这是正确的。 C 和 C++ 需要一个名为 main 的独立函数，该函数返回 int。拥有一个名为main 的方法的类 是不够的；编译器只关心独立的。

另一件事要记住，class 类型中成员的默认可见性是private。要么将您的类更改为使用 struct(这几乎是两者之间的唯一区别)，要么指定公共(public)可见性:

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

然后你可以从你的类中调用main函数:

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