刚开始 C++：编译时出现未定义符号错误答案

【问题标题】：Just started C++: Undefined Symbol error on Compile刚开始 C++：编译时出现未定义符号错误
【发布时间】：2009-02-08 23:36:29
【问题描述】：

情况如下：

我刚刚开始了我的第一个 C++ 课程。我对 C++ 一无所知，尽管这是 C++ 课程的介绍，但老师几乎没有教过该语言的语法，只是我们已经知道的逻辑。

现在他给了我们一个程序描述并说，“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 编写了它（我确实知道），然后一旦我让它在 java 中工作，我就尝试将它编码为 C++。

但是现在我在编译时遇到以下错误

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();
        }
};

【问题讨论】：

标签： c++ compilation

【解决方案1】：

它抱怨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。

要记住的另一件事是class 类型中成员的默认可见性是私有。要么改变你的班级以使用struct——这几乎是两者之间的唯一区别——要么指定公开可见性：

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;
}

【讨论】：

默认访问级别很好。

【解决方案2】：

你需要一个 main() 函数来给程序一个起点：

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

     Race race;

     race.main();
}

但是让您的许多方法成为静态方法可能是有意义的，因为它们不依赖于 Race 类的任何实例成员。

【讨论】：

如果你打算使用静态方法，我倾向于只使用函数。也许在命名空间中。
你不会从我这里得到任何论据。

【解决方案3】：

你需要一个主函数：

// 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();
}

左右，没有看到你的具体错误。

【讨论】：

【解决方案4】：

C++ 与 Java 完全不同。例如，函数不必是类的一部分。您需要移动函数 main() 使其位于类之外。

class Race {
  // stuff
};

int main() {
  // stuff
}

【讨论】：

【解决方案5】：

也许这就是你的意思

#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();
}

【讨论】：

函数 main 总是返回 int，从不为 void。把它当作陈词滥调的人会因此评判你，你的程序会有未定义的行为。
“把它当作陈词滥调的人”哈哈哈好。我只是使用与 OP 相同的代码，以便他知道去哪里。

【解决方案6】：

你没有主函数。

C++与Java最大的不同在于它的main()函数有这样的签名（参数可选）：

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

而且它在全局命名空间中。这是程序启动时调用的函数，可能是您缺少符号的原因。

尝试将其添加到您的程序中：

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

或者，您可以完全取消该类，因为您实际上并没有对它做任何事情。

【讨论】：