关于C++ new 的实验

#include <iostream>

using namespace std;

class Anew
{
public:
    int a;
    Anew()
    {}
};

class Bnew
{
public:
    int a;
    Bnew():a(100)
    {}
};

class Cnew
{
public:
    int a;
};


int main(int argc, char *argv[])
{
    Anew tmp1;
    Anew* tmp2 = new Anew;
    Anew* tmp3 = new Anew();
    cout << tmp1.a<<endl;
    cout << tmp2->a<<endl;
    cout << tmp3->a<<endl;

    Bnew tmp11;
    Bnew* tmp22 = new Bnew;
    Bnew* tmp33 = new Bnew();
    cout << tmp11.a<<endl;
    cout << tmp22->a<<endl;
    cout << tmp33->a<<endl;

    Cnew tmp111;
    Cnew* tmp222 = new Cnew;
    Cnew* tmp333 = new Cnew();
    cout << tmp111.a<<endl;
    cout << tmp222->a<<endl;
    cout << tmp333->a<<endl;

    return 0;
}

g++ 8.1.0

输出：

0

-1163005939

-1163005939

100

100

100

2046

-1163005939

0

Anew　　手动写了构造函数

Bnew　　手动写了构造函数并有数值初始化

Cnew　　编译器自带的构造函数