I am trying to create an array of pointers. These pointers will point to a Student object that I created. How do I do it? What I have now is:
Student * db = new Student[5];
But each element in that array is the student object, not a pointer to the student object. Thanks.
Student** db = new Student*[5];
// To allocate it statically:
Student* db[5];
Student* db[5] the same thing as Student** db = new Student*[5]? What is the benefit of using one over the other?
#include <vector>
std::vector <Student *> db(5);
// in use
db[2] = & someStudent;
The advantage of this is that you don't have to worry about deleting the allocated storage - the vector does it for you.
An array of pointers is written as a pointer of pointers:
Student **db = new Student*[5];
Now the problem is, that you only have reserved memory for the five pointers. So you have to iterate through them to create the Student objects themselves.
In C++, for most use cases life is easier with a std::vector.
std::vector<Student*> db;
Now you can use push_back() to add new pointers to it and [] to index it. It is cleaner to use than the ** thing.
If the size of the array is known at compile time, I tend to use std::array
class Student {
public:
Student() {
std::cout << "Student Created\n";
}
~Student() {
std::cout << "Student Deleted\n";
}
int a;
};
int main() {
std::array<Student*, 5> arr;
arr[1] = new Student();
arr[1]->a = 42;
std::cout << arr[1]->a << std::endl;
delete arr[1]; // Don't forget to call the destructor
return 0;
}
Output:
Student Created
42
Student Deleted
Note, that arr won't initialize elements to nullptr, might contain memory garbage. Also, don't forget to clean up when you're done.
Better approach would be to use RAII as follows:
class Student {
public:
Student() {
std::cout << "Student Created\n";
}
~Student() {
std::cout << "Student Deleted\n";
}
int a;
};
int main() {
std::array<std::unique_ptr<Student>, 5> arr;
arr[1] = std::make_unique<Student>();
arr[1]->a = 42;
std::cout << arr[1]->a << std::endl;
// No delete needed here, unique_ptr will take care of lifetime management
return 0;
}
Same output, but safer:
Student Created
42
Student Deleted
void main()
{
int *arr;
int size;
cout<<"Enter the size of the integer array:";
cin>>size;
cout<<"Creating an array of size<<size<<"\n";
arr=new int[size];
cout<<"Dynamic allocation of memory for memory for array arr is successful";
delete arr;
getch();enter code here
}
