Dynamic memory

[radiat]

Just studying dynamic memory at the minute. I understand the idea of having dynamic memory for arrays so you can set the length of them within the running of the program. But what is the point of dynamic memory for a single type? If i set an 'int' up to have dynamic memory is it still not limited by the amount of memory assigned to an int ie. 4 bytes?

Random Question: What colour was George Washington's white horse?
Me : How the hell would i know what col.... Oh!

[deceptikon]

One example: You may want the lifetime of the object to not be restricted to the scope in which it was declared. Dynamic memory has a lifetime of when you allocate it to when you release it.

[Moschops]

But what is the point of dynamic memory for a single type?

What would you prefer? A minimum size permitted for dynamic memory?

[radiat]

Do you mean if i were to declare an object with dynamic memory within a particular function it would be available within another function?

[mike_2000_17]

>>Do you mean if i were to declare an object with dynamic memory within a particular function it would be available within another function?

Yes, if you provide the pointer as a result of the function for example.

Generally, this is not recommended, but sometimes hard to avoid. If you do that, it is also recommended that you use a smart-pointer instead of a simple pointer (or raw pointer).

In concrete terms:

int* give_pointer() {
  return new int(42);
};

int main() {
  int* pi = give_pointer();
  
  // now, the value can be accessed from outside the function, through pi:
  std::cout << " The value is: " << *pi << std::endl;
  
  // now, here's the nasty part, you have to delete the pointer yourself:
  delete pi;  //But, what if it was created with malloc()? What if it was a static variable? This line could cause a crash...
  return 0;
};

Normally, you would, instead, provide an additional function to deallocate the object. The point of all this is that the life-time of the object is from point of the "new" call up to the point of the "delete" call, so, it is not bound to an automatic scope like local variables (which, simply speaking, are created when you enter the function and get destroyed when you leave it).

Better yet, you use a smart-pointer whose job is to delete the object when noone needs it anymore (this is what std::shared_ptr does).

Another use for allocating one object at a time is for doing dynamic polymorphism, e.g., to create an object of one class and provide it as a base-class pointer. But I have the feeling you are not there yet in your learning / book-reading, so, leave that aside for now.

[WaltP]

But what is the point of dynamic memory for a single type?

Exactly...
For a single type, it's a waste to use dynamic memory. I can't think of any reason why one would need to dynamically create an int or float.

Do you mean if i were to declare an object with dynamic memory within a particular function it would be available within another function?

If you pass it to the function, sure...

[radiat]

ok, thanks for your help