一个简单的C++语法问题。

[richoboy]

#include <iostream.h>

class A
{
public:
A()
{
cout << "this is A" << endl;
}
~A(){}

void outputA()
{
cout << "outputA" << x << y << endl;
}
int x;
int y;
};

class B
{
public:
B()
{
cout << "this is B" << endl;
pA = NULL;
}
~B(){}

void outputB(int m,int n)
{
cout << "outputB" << endl;
pA->x=m;
pA->y=n;
pA->outputA();
}
A *pA;
};

int main()
{

B cB;
cB.outputB(4,3);
cout << cB.pA->x << endl << cB.pA->y << endl;
return 0;
}


这个代码在哪里出现了问题？怎么解决。谢谢了

[richoboy]

#include <iostream.h>

class A
{
public:
    A()
   {
        cout < < "this is A" < < endl;
   }
   ~A(){}

    void outputA()
   {  
       cout < < "outputA" < < x < < y < < endl;
   }
   int x;
   int y;
};

class B
{
public:
    B()
   {
       cout < < "this is B" < < endl;
       pA = NULL;
   }
   ~B(){}

   void outputB(int m,int n)
  {
       cout < < "outputB" < < endl;
       pA->x=m;
       pA->y=n;
       pA->outputA();
   }
   A *pA;
};

int main()
{

    B cB;
    cB.outputB(4,3);
    cout < < cB.pA->x < < endl < < cB.pA->y < < endl;
    return 0;
} 

[lionc650]

void outputA()
{
cout < < "outputA" < < x < < y < < endl;
}
int x;
int y;
};

void outputB(int m,int n)
{
cout < < "outputB" < < endl;
pA->x=m;
pA->y=n;
pA->outputA();
}
A *pA;
};

这都什么跟什么啊...... x，y可不是A的成员。 建议楼主看看面向对象的基础..

[美伊小公主的奶爸]

class B
{
public:
B()
{
cout < < "this is B" < < endl;
pA = NULL;
}
~B(){}
中的pA是什么类型？当然会出错了 ！

[lionc650]

晕，看错了。。。lz这排版太难看了....

[richoboy]

[Quote=引用 1 楼 richoboy 的回复:]
C/C++ code#include<iostream.h>classA
{public:
A()
{
cout<<"this is A"<<endl;
}~A(){}voidoutputA()
{
cout<<"outputA"<<x<<y<<endl;
}intx;inty;
};classB
{public:
B()
{
cout<<"this is B"<<endl;
pA=NULL;
}~B(){}voidoutputB(intm,intn)
{
cout<<"outputB"<<endl;
pA->x=m;
pA->y=n;
pA->outputA();
}
A*pA;
};intmain(…
[/Quote]

为什么不是啊，我在A中定义了x，y二个成员啊.

[richoboy]

[Quote=引用 3 楼 cymvp 的回复:]
class B
{
public:
B()
{
cout < < "this is B" < < endl;
pA = NULL;
}
~B(){}
中的pA是什么类型？当然会出错了 ！
[/Quote]
这个是给pA初始化啊，让他指向空。

[zclever]

#include <iostream.h> 

class A 
{ 
public: 
A() 
{ 
cout << "this is A" << endl; 
} 
~A(){} 

void outputA() 
{ 
cout << "outputA" << x << y << endl; 
} 
int x; 
int y; 
}; 

class B 
{ 
public: 
B() 
{ 
cout << "this is B" << endl; 
//pA = NULL; 
pA=new A; //记得给A分配空间
} 
~B(){delete pA;} //删除空间

void outputB(int m,int n) 
{ 
cout << "outputB" << endl; 
pA->x=m; 
pA->y=n; 
pA->outputA(); 
} 
A *pA; 
}; 

int main() 
{ 

B cB; 
cB.outputB(4,3); 
cout << cB.pA->x << endl << cB.pA->y << endl; 
return 0; 
} 

[美伊小公主的奶爸]

你的pA没有指向实际对象阿，一直是null,所以会出错阿

[sk19891117]

void outputB(int m,int n)
{
cout < < "outputB" < < endl;
pA->x=m;
pA->y=n;
pA->outputA();
}
A *pA;



把A *pA放前面会不会好点呢？（不成熟的意见）

[zhouqiang714]

#include <iostream>
using namespace std;

class A
{
public:
A()
{
cout << "this is A"<<endl;
}
~A(){}

void outputA()
{
cout << "outputA" << x << y << endl;
}
int x;
int y;
};

class B :public A
{

public:
B()
{
cout<< "this is B"<< endl;
}
~B(){}
void outputB(int m,int n)
{
cout<< "outputB"<< endl;
pA.x=m;
pA.y=n;
pA.outputA();
}
A pA;
};

int main()
{

B cB;
cB.outputB(4,3);
cout<< cB.pA.x<< endl<< cB.pA.y<< endl;
system("pause");
return 0;
}

[handsomezwm]

#include <iostream.h>

class A
{
public:
A()
{
cout << "this is A" << endl;
}
~A(){}

void outputA()
{
cout << "outputA" << x << y << endl;
}
int x;
int y;
};

class B
{
public:
B()
{
cout << "this is B" << endl;
pA = new A(); //问题出现在这个地方，程序中PA是一个空指针，所以你不能为其赋值，而给他一个
} //分配一个指向的空间就OK了
~B(){}

void outputB(int m,int n)
{
cout << "outputB" << endl;
pA->x=m;
pA->y=n;
pA->outputA();
}
A *pA;
};

int main()
{

B cB;
cB.outputB(4,3);
cout << cB.pA->x << endl << cB.pA->y << endl;
return 0;
}