Issue on using multiple structures by pointers cause crash on program executing-CodePudding

Hello I noticed this weird issue when using multiple pointer structures at the same time. Can somebody explain to me what is causing it ?

#include <iostream>

using namespace std;

typedef struct A{
    int x;
}a;

int main()
{
    a *a1, *a2;
    a1->x = 3;
    cout << a1->x << endl; // display "3"
    
    a2->x = 2;
    cout << a2->x << endl; // ...does not display "2" ???

    return 0;
}

CodePudding user response：

Before assigning the values to your pointers, the pointers have to be initialized properly.

a *a1, *a2;

These pointers are not initialized. They point to some random location in memory. The "new" keyword allocates memory for your structure. You can use it like this:

a *a1 = new A, *a2 = new A;