c++-构造函数练习和delete，new

强化练习

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <iostream>
#include <fstream>
using namespace std;

class   abcd
{
public:
    abcd(int    a, int  b, int  c)
    {
        _a = a;
        _b = b;
        _c = c;
        printf("abcd()  construct,  a: %d,b: %d,c: %d        \n", _a, _b, _c);
    }
    ~abcd()
    {
        printf("~abcd() construct,a: %d,b: %d,c: %d      \n", _a, _b, _c);
    }
    int geta()
    {
        return  _a;
    }
private:
    int _a;
    int _b;
    int _c;
};

class   mye
{
public:

    mye() :abcd1(1, 2, 3), abcd2(4, 5, 6), m(100)
    {
        cout << "mye()" << endl;
    }
    ~mye()
    {
        cout << "~mye()" << endl;
    }

    mye(const   mye &   obj) :abcd1(7, 8, 9), abcd2(10, 11, 12), m(100)
    {
        printf("myd(const   myd &   obj) \n");
    }
public:
    abcd    abcd1;   //c++编译器不知道如何构造abc1
    abcd    abcd2;
    const int   m;
};

int dothing(mye mye1)//mye1.拷贝构造(main::mye)
{
    printf("dothing()   mye1.abc1.a: %d \n", mye1.abcd1.geta());
    return 0;
}
int run()
{
    mye mye;
    dothing(mye);
    return 0;
}

int run2()
{
    printf("run2    start.. \n");
    //abcd(400, 500, 600);   //临时对象的⽣命周期        
    abcd    abcd    =   abcd(100,   200,    300);
    printf("run2    end\n");
    return 0;
}

int main(void)
{
    run2();
    return 0;
}

强化练习2

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <iostream>
#include <fstream>
using namespace std;

//构造中调⽤构造是危险的⾏为
class   mytest
{
public:
    mytest(int  a, int  b, int  c)
    {
        _a = a;
        _b = b;
        _c = c;
    }
    mytest(int  a, int  b)
    {
        _a = a;
        _b = b;
        mytest(a, b, 100);//创建一个匿名对象
        //
    }
    ~mytest()
    {
        printf("mytest~: %d,     %d,     %d\n", _a, _b, _c);
    }
    int getc()
    {
        return  _c;
    }
    void    setc(int    val)
    {
        _c = val;
    }

private:
    int _a;
    int _b;
    int _c;
};

int main()
{
    mytest  t1(1, 2);
    printf("c: %d\n", t1.getc());    //请问c的值是？
    return 0;
}

• 对象的动态构造和释放
  • malloc free函数，new delete 操作符号
  • 分配基础类型 、分配数组类型、分配对象
  • new和malloc 深入分析，混用测试、异同比较
• 匿名对象生命周期
• malloc free函数，new delete 操作符号
• 分配基础类型 、分配数组类型、分配对象
• new和malloc 深入分析，混用测试、异同比较
• 匿名对象总结
  • 匿名对象生命周期
  • 匿名对象去和留
  • 构造中调用构造
• 匿名对象去和留
• 构造中调用构造
• 静态成员变量和静态成员函数（属于类，语法）

new和delete

c与c++的比较

#define _crt_secure_no_warnings
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <iostream>
#include <fstream>


using namespace std;

class test
{
public:
    test()
    {
        cout << "test()" << endl;
        m_a = 0;
        m_b = 0;
    }
    test(int a, int b)
    {
        cout << "test(int, int)" << endl;
        m_a = a;
        m_b = b;
    }
    void printt()
    {

        cout << "printt:"<<m_a<<","<<m_b << endl;
    }
    ~test()
    {
        cout << "~test()" << endl;

    }
private:
    int m_a;
    int m_b;
};

//c语言中
void test1()
{
    int *p = (int *)malloc(sizeof(int));

    *p = 10;
    if (p != null) {
        free(p);
        //delete p;
        p = null;
    }

    int *array_p = (int *)malloc(sizeof(int)* 10);

    for (int i = 0; i < 10; i++) {
        array_p[i] = i + 1;
    }

    for (int i = 0; i < 10; i++) {
        printf("%d ", array_p[i]);
    }
    printf("\n");

    if (array_p != null) {
        free(array_p);
        array_p = null;
    }


    cout << "==============" << endl;

    test *tp = (test*)malloc(sizeof(test));
    tp->printt();

    if (tp != null) {
        free(tp);
        tp = null;
    }
}

//malloc free 是函数，标准库，stdlib.h
//new 在堆上初始化一个对象的时候，会触发对象的构造函数。malloc不能
//free并不能触发一个对象的析构函数。
//c++中
void test2()
{
    int *p = new int;
    *p = 10;
    if (p != null) {
        free(p);
        p = null;
    }

    int *array_p = new int[10];
    for (int i = 0; i < 10; i++) {
        array_p[i] = i + 1;
    }

    for (int i = 0; i < 10; i++) {
        cout << array_p[i]<<" ";
    }
    cout << endl;

    if (array_p != null) {
        delete [] array_p;
    }

    cout << "==========" << endl;
    //test *tp = new test(10, 20);//触发有参构造
    test *tp = new test;//触发无惨构造
    tp->printt();
    if (tp != null) {
        delete tp;
        tp = null;
    }

}

int main(void)
{
    test1();

    cout << "-----------" << endl;

    test2();
    
    return 0;
}