5.构造函数

1.构造函数就是对象的初始化

class complex{
    private:
        double real,imag;
    public:
        complex(double r,doublei=0);
};
complex::complex(double r,double i){
    real=r;imag=i;
}
complex c1; //error,缺少构造函数参数
complex *pc=new complex; //error,没有参数
complex c1(2);//ok
complex c1(2,4),c2(3,5);//ok
complex *pc=new complex(3,4);//ok

2.一个类可以有多个构造函数，参数个数或者类型不同。

complex::complex(double r)
{
    real=r;imag=0;
}
complex::complex(complex c1,complex c2)
{
    real=c1.real+c2.real;
    imag=c1.imag+c2.imag;
}
complex c1(3),c2(1,0),c3(c1,c2);
//c1={3,0},c2={1,0},c3={4,0};

3.构造函数初始化重载的例子

class csample
{
    int x;
    public:
        csample(){
            cout<<"constructor 1 call"<<end;
        }
        csample(int n)
        {
            x=n;
            cout<<"constructor 2 called"<<endl;
        }
};
int main()
{
    csample array1[2];
    cout<<"step"<<endl;
    csample array2[2]={4,5};
    cout<<"step2"<<endl;
    csample array3[2]={3};
    cout<<"step3"<<endl;
    csample *array4=new csample[2];
    delete []array4;
    return 0;
}
/*输出：
constructor 1 called
constructor 1 called
step1
constructor 2 called
constructor 2 called
step 2
constructor 2 called
constructor 1 called
step3 */

4.构造函数在数组中的使用

class test{
    public:
        test(int n){} //1
        test(int n,int m)  //2
        test(){}  //3
};
test array[3]={1,test(1,2)};  //三个元素分别用1，2，3初始化
test array[3]={test(2,3),test(1,2),1}; //三个元素分别用2，2，1初始化
test *parray[3]={new test(4),new test(1,2)};