I wonder why the second part of the following code I wrote doesn't work. I am practicing vector of pointers to class objects. I tried two ways, one is to define a class object; the other is to define a pointer to the object. The second way failed.
#include <iostream>
#include <vector>
using namespace std;
class A{
public:
int id;
A(int id):id(id){}
};
int main()
{
vector<A*> A_vec, A_vec2;
A a(5);
A_vec.push_back(&a);
cout << A_vec.size() << "; id " << A_vec[0]->id << endl;
A *a1;
a1->id = 5;
A_vec2.push_back(a1);
cout << A_vec2.size() << "; id " << A_vec2[0]->id << endl;
}
The second snippet doesn't work because you've never allocated memory for the object, so a1
points nowhere.
A *a1 = new A(5);
...
// Once you're done with `a1', release the memory.
delete a1;
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