C++构造函数理解

 正确理解Qt中构造函数：Widget::Widget(QWidget *parent) : QWidget(parent),ui(new Ui::Widget)

#include <iostream>

using namespace std;

class Base
{
    public:
        Base():m_num(0){
            cout << "this is Base()" << endl;
        }
        Base(int val):m_num(val + 1){
            cout << "this is Base(int val) and m_num = " << m_num << endl;
        }

    private:
        int m_num;
};

class BaseChild : public Base
{
    public:
        BaseChild(){
            cout << "this is BaseChild()" << endl;
        }
        BaseChild(int val) : Base(val), m_num(val){
            cout << "this is BaseChild(int val) and m_num = " << m_num << endl;
        }

    private:
        int m_num;
};

int main(int argc, char *argv[])
{
    BaseChild child1;
    BaseChild child2(5);

    return 0;
}

输出结果：

this is Base()
this is BaseChild()
this is Base(int val) and m_num = 6
this is BaseChild(int val) and m_num = 5

BaseChild是类, ::是作用域，::后面的BaseChild(int val)是构造函数，：后面的Base(val)是指定基类的构造函数，不明确指定的话是默认构造函数，n_num(val) 是对BaseChild类里面的成员变量做初始化。

 

Widget::Widget(QWidget *parent) : QWidget(parent),ui(new Ui::Widget)
理解：
    Widget是类, ::是作用域，::后面的Widget(QWidget *parent)是构造函数，
    ：后面的 QWidget(parent)是指定基类的构造函数，不明确指定的话是默认构造函数，
    ui(new Ui::Widget) 是对BaseChild类里面的成员变量做初始化。

本文借鉴：https://blog.csdn.net/qq_41827665/article/details/84213220

来源：CSDN

作者：GouplovXim1314

链接：https://blog.csdn.net/GouplovXim1314/article/details/104349423