C++ FAQ Celebrating Twenty-One Years of the C++ FAQ!!!
(Click here for a personal note from Marshall Cline.)
Section 16:
16.1 Does delete p delete the pointer p, or the pointed-to-data *p?
16.2 Is it safe to delete the same pointer twice?
16.3 Can I free() pointers allocated with new? Can I delete pointers allocated with malloc()?
16.4 Benefits of new over malloc()?
16.5 Can I use realloc() on pointers allocated via new?
16.6 Checking for NULL after p = new Fred()?
16.7 How can I convince my (older) compiler to automatically check new to see if it returns NULL?
16.8 Checking for NULL before delete p?
16.9 What are the two steps that happen when I say delete p?
16.10 Does p = new Fred() leak memory if the ctor throws an exception?
16.11 How do I allocate / unallocate an array of things?
16.12 What if I forget the [] when deleteing an array allocated via new T[n]?
16.13 Can I drop the [] when deleteing an array of some built-in type (char, int, etc)?
16.14 After p = new Fred[n], how does the compiler know there are n objects to be destructed during delete[] p?
16.15 Is it legal (and moral) for a member function to say delete this?
16.16 How do I allocate multidimensional arrays using new?
16.17 How to simplify the Matrix code from the previous FAQ?
16.18 How to make the Matrix class generic?
16.19 What's another way to build a Matrix template?
16.20 Does C++ have arrays whose length can be specified at run-time?
16.21 Allocating all objects via new, not local/global/static?
16.22 How do I do simple reference counting?
16.23 How do I provide reference counting with copy-on-write semantics?
16.24 How do I provide reference counting with copy-on-write semantics for a hierarchy of classes?
16.25 Preventing people from subverting the reference counting mechanism?
16.26 Can I use a garbage collector in C++?
16.27 What are the two kinds of garbage collectors for C++?
16.28 Where can I get more info on garbage collectors for C++?
[16.21] How can I force objects of my class to always be created via new rather than as locals or global/static objects?

Use the Named Constructor Idiom.

As usual with the Named Constructor Idiom, the constructors are all private or protected, and there are one or more public static create() methods (the so-called "named constructors"), one per constructor. In this case the create() methods allocate the objects via new. Since the constructors themselves are not public, there is no other way to create objects of the class. 

class Fred {
public:
  // The create() methods are the "named constructors":
  static Fred* create()                 { return new Fred();     }
  static Fred* create(int i)            { return new Fred(i);    }
  static Fred* create(Fred const& fred) { return new Fred(fred); }
  ...

private:
  // The constructors themselves are private or protected:
  Fred();
  Fred(int i);
  Fred(Fred const& fred);
  ...
};
Now the only way to create Fred objects is via Fred::create(): 
int main()
{
  Fred* p = Fred::create(5);
  ...
  delete p;
  ...
}
Make sure your constructors are in the protected section if you expect Fred to have derived classes.

Note also that you can make another class Wilma a friend of Fred if you want to allow a Wilma to have a member object of class Fred, but of course this is a softening of the original goal, namely to force Fred objects to be allocated via new.