C++之构造函数默认值设置方式

#include <iostream>
using namespace std;
class CTest
{
public:    
    CTest();
    CTest(int _a, double _b, const bool _c = false, bool _d = true);
private:
    const bool c;
    bool d;
    int a;
    double b; 
};
CTest::CTest(int _a, double _b = 1.0, const bool _c,  bool _d):a(_a), b(_b), c(_c), d(_d)
{
    cout << a << endl;
    cout << b << endl;
    cout << c << endl;
    cout << d << endl;  
}
int main()
{
    // CTest* test = new CTest(1, 1.0, true, false);
    // CTest* test = new CTest(1, 1.0, true);
    //CTest* test = new CTest(1, 1.0);
    CTest* test = new CTest(1);
    return 0;
}

#include <iostream>
using namespace std;
class Box{
public:
    Box(int h=2,int w=2,int l=2);//在声明构造函数时指定默认参数
    int volume();
private:
    int height,width,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(1);//不指定第2、3个实参
    cout<<"box1's volume: "<<box1.volume()<<endl;
    Box box2(1,3);// 不指定第3个实参
    cout<<"box2's volume: "<<box2.volume()<<endl;
    Box box3;
    cout<<"box3's volume:"<<box3.volume()<<endl;
    return 0;
}

[root@localhost charpter02]# ./0210
box1's volume: 4
box2's volume: 6
box3's volume:8

Box(int =10,int=3,int=5);
Box();
Box(int,int);

Box box1；              //是应该调用第1个构造函数还是应该调用第2个构造函数
Box box2(13,18);        //是应该调用第2个构造函数还是应该调用第3个构造函数