#include<iostream>
原始代码(出错代码）为：
#include<string>
using namespace std;
class Point
{
      protected:
              int x,y;
      public:
             void draw(int a,int b)
             {
                  x=a;
                  y=b;
             }
             void show()
             {
                  cout<<"This point is the abscissa for "<<x<<", y coordinate for"<<y<<endl;
             }
};
class colour_Point : public Point
{
      private:
              char colour;
      public:
              virtual void draw(int m,int n,char &q)
             {
                  x=m;
                  y=n;
                  colour=q;
             }
             virtual void show()
             {
                  cout<<"This point is the abscissa for "<<x<<", y coordinate for"<<y<<endl;
                  cout<<"And the Point's colour is   "<<colour<<endl;
             }
};


int main()
{
    Point point;
    point.draw(3,4);
    point.show();
    colour_Point colour_point;
    colour_point.draw(4,5,"紫色");
    colour_point.show();
    system("pause");
    return 0;
}
    //以上代码编译出错，出错原因：字符串字长限制。
   
   修改方案：将地址引用，换成指针传递变量。

修改成功的代码为：
#include<iostream>
#include<string>
using namespace std;
class Point
{
      protected:
              int x,y;
      public:
             void draw(int a,int b)
             {
                  x=a;
                  y=b;
             }
             void show()
             {
                  cout<<"This point is the abscissa for "<<x<<", y coordinate for"<<y<<endl;
             }
};
class colour_Point : public Point
{
      private:
              char *colour;
      public:
              virtual void draw(int m,int n,char *q)
             {
                  x=m;
                  y=n;
                  colour=q;
             }
             virtual void show()
             {
                  cout<<"This point is the abscissa for "<<x<<", y coordinate for"<<y<<endl;
                  cout<<"And the Point's colour is   "<<colour<<endl;
             }
};


int main()
{
    Point point;
    point.draw(3,4);
    point.show();
    colour_Point colour_point;
    colour_point.draw(4,5,"紫色");
    colour_point.show();
    system("pause");
    return 0;
}
   编译结果为：    This point is the abscissa for  3 , y coordinate for 4   
                   This point is the abscissa for  4 ，y coordinate for 5，and the Point's colour is 紫色

地址引用与指针传递的区别吧。程序运行前后有明显的修改之处。

字长限制是程序运行后指定的错误，不过你的建议我会好好看看的呢。