解析C++中构造函数的默认参数和构造函数的重载

#include <iostream>
using namespace std;
class Box
{
  public :
  Box(int h=10,int w=10,int len=10); //在声明构造函数时指定默认参数
  int volume( );
  private :
  int height;
  int width;
  int length;
};
Box::Box(int h,int w,int len) //在定义函数时可以不指定默认参数
{
  height=h;
  width=w;
  length=len;
}
int Box::volume( )
{
  return (height*width*length);
}
int main( )
{
  Box box1; //没有给实参
  cout<<"The volume of box1 is "<<box1.volume( )<<endl;
  Box box2(15); //只给定一个实参
  cout<<"The volume of box2 is "<<box2.volume( )<<endl;
  Box box3(15,30); //只给定2个实参
  cout<<"The volume of box3 is "<<box3.volume( )<<endl;
  Box box4(15,30,20); //给定3个实参
  cout<<"The volume of box4 is "<<box4.volume( )<<endl;
  return 0;
}

The volume of box1 is 1000
The volume of box2 is 1500
The volume of box3 is 4500
The volume of box4 is 9000

  Box::Box(int h,int w,int len):height(h),width(w),length(len){ }

#include <iostream>
using namespace std;
class Box
{
  public : Box( ); //声明一个无参的构造函数
  //声明一个有参的构造函数，用参数的初始化表对数据成员初始化
  Box(int h,int w,int len):height(h),width(w),length(len){ }
  int volume( );
  private :
  int height;
  int width;
  int length;
};
Box::Box( ) //定义一个无参的构造函数
{
  height=10; width=10; length=10;
}
int Box::volume( ){
  return (height*width*length);
}
int main( )
{
  Box box1; //建立对象box1,不指定实参
  cout<<"The volume of box1 is "<<box1.volume( )<<endl;
  Box box2(15,30,25); //建立对象box2,指定3个实参
  cout<<"The volume of box2 is "<<box2.volume( )<<endl;
  return 0;
}

  Box::Box(int h); //有1个参数的构造函数
  Box::Box(int h,int w); //有两个参数的构造函数