类对象成员的初始化

#include<bits/stdc++.h>
using namespace std;
/**
 * 类对象成员初始化
 * */
class StudentID {
    public:
        int getID() {
            return value;
        }
        StudentID(int id=0) {
            value = id;
            printf("student id: %d\n", value);
        }
        ~StudentID() {
            printf("destruct id: %d\n", value);
        }
    private:
        int value;
};
class Student {
    char name[20];
    StudentID id; 
    public:
        Student(char *pName="noName", int ssID = 0): id(ssID) {
            printf("construct student %s\n", pName);
            strncpy(name, pName, sizeof(name));
            name[sizeof(name)-1] = '\0';
            // StudentID(ssID); // 错误，实际上定义了一个对象成员，但是之前已经调用了默认的构造函数了
        }
        ~Student() {
            printf("destruct name %s id: %d\n", name, id.getID());
        }
        void display() {
            printf("student name:%s id: %d\n", name, id.getID());
        }
};  
int main() {
    char name[20] = "console";
    Student s(name, 2019);
    s.display();
    return 0;
}

类对象成员的构造顺序

#include<bits/stdc++.h>
using namespace std;
/**
 * 类对象成员的构造顺序
 * */
class A {
    int a;
    public:
        A(int i) {
            a = i;
            printf("construct A a=%d\n", a);
        }
};
class B {
    int b;
    public:
        B(int i) {
            b = i;
            printf("construct B b=%d\n", b);
        }
};
class C {
    A a1, a2;
    B b1, b2;
    public:
        C(int i1, int i2, int i3, int i4) :b1(i1), a1(i2), b2(i3), a2(i4) {
        }
};
int main() {
    C x(1, 2, 3, 4);
    return 0;
}

输出顺序应该是声明顺序，而不是构造函数中初始化列表的顺序
2 4 1 3