学习C++一疑问（有关函数定义位置的问题）？

Question

书上面说可以在类定义外定义函数，但是小弟用VC试验的时候 发现却不可以程序如下：这个是书上给出的 但是运行通不过“void rectangle::assign(double len,double wide){length=len;width=wide;}”就是要定义的函数，如果将其写在类 rectangle定义中则可以运行 程序：#include<iostream.h>class rectangle{protected:double length;double width;public:rectangle(){assign(0,0);}rectangle(double len,double wide){assign(len,wide);}double getLength(){return length;}double getWidth(){return width;}double getArea(){return length*width;}};void rectangle::assign(double len,double wide){length=len;width=wide;}main(){rectangle rect;double len,wide;cout<<"enter length of rectangle:";cin>>len;cout<<"enter width of rectangle:";cin>>wide;rect.assign(len,wide);cout<<"rectangle length="<<rect.getLength()<<"\n"<<" width ="<<rect.getWidth()<<"\n"<<" area ="<<rect.getArea()<<"\n";return 0;}

Answer 1

正确的程序为：
#include<iostream.h>
class rectangle
{
protected:
double length;
double width;
public:
rectangle::assign(double len,double wide);
rectangle(){assign(0,0);}
rectangle(double len,double wide){assign(len,wide);}
double getLength(){return length;}
double getWidth(){return width;}
double getArea(){return length*width;}
};
rectangle::assign(double len,double wide)
{
length=len;width=wide;
}

int main()
{
rectangle rect;
double len,wide;
cout<<"enter length of rectangle:";
cin>>len;
cout<<"enter width of rectangle:";
cin>>wide;
rect.assign(len,wide);
cout<<"rectangle length="<<rect.getLength()<<"\n"
<<" width ="<<rect.getWidth()<<"\n"
<<" area ="<<rect.getArea()<<"\n";
return 0;
}
在类定义外定义函数时需在类内做函数声明。
另void rectangle::assign(double len,double wide) 类声明重复，这里rectangle是定义的类，是你需要的，所以void不要。还有main( )前必须有类声明，这里为int。

Answer 2

将
void rectangle::assign(double len,double wide)
{
length=len;width=wide;
}
改为：
inline void rectangle::assign(double len,double wide)
{
length=len;width=wide;
}
试试
加上inline的意思是：将rectangle函数作为类的内联函数