# Coin::SmartPtr< T > Class Template Reference

Template class for Smart Pointers. More...

`#include <CoinSmartPtr.hpp>`

List of all members.

## Public Member Functions
T * | GetRawPtr () const
| Returns the raw pointer contained.
bool | IsValid () const
| Returns true if the SmartPtr is NOT NULL.
bool | IsNull () const
| Returns true if the SmartPtr is NULL.
Constructors/Destructors
| SmartPtr ()
| Default constructor, initialized to NULL.
| SmartPtr (const SmartPtr< T > &copy)
| Copy constructor, initialized from copy.
| SmartPtr (T *ptr)
| Constructor, initialized from T* ptr.
| ~SmartPtr ()
| Destructor, automatically decrements the reference count, deletes the object if necessary.
## Private Data/Methods
T * | ptr_
| Actual raw pointer to the object.
void | ReleasePointer_ ()
| Release the currently referenced object.
SmartPtr< T > & | SetFromRawPtr_ (T *rhs)
| Set the value of the internal raw pointer from another raw pointer, releasing the previously referenced object if necessary.
SmartPtr< T > & | SetFromSmartPtr_ (const SmartPtr< T > &rhs)
| Set the value of the internal raw pointer from a SmartPtr, releasing the previously referenced object if necessary.
## Overloaded operators.
T * | operator-> () const
| Overloaded arrow operator, allows the user to call methods using the contained pointer.
T & | operator* () const
| Overloaded dereference operator, allows the user to dereference the contained pointer.
SmartPtr< T > & | operator= (T *rhs)
| Overloaded equals operator, allows the user to set the value of the SmartPtr from a raw pointer.
SmartPtr< T > & | operator= (const SmartPtr< T > &rhs)
| Overloaded equals operator, allows the user to set the value of the SmartPtr from another SmartPtr.
template<class U1 , class U2 >
bool | operator== (const SmartPtr< U1 > &lhs, const SmartPtr< U2 > &rhs)
| Overloaded equality comparison operator, allows the user to compare the value of two SmartPtrs.
template<class U1 , class U2 >
bool | operator== (const SmartPtr< U1 > &lhs, U2 *raw_rhs)
| Overloaded equality comparison operator, allows the user to compare the value of a SmartPtr with a raw pointer.
template<class U1 , class U2 >
bool | operator== (U1 *lhs, const SmartPtr< U2 > &raw_rhs)
| Overloaded equality comparison operator, allows the user to compare the value of a raw pointer with a SmartPtr.
template<class U1 , class U2 >
bool | operator!= (const SmartPtr< U1 > &lhs, const SmartPtr< U2 > &rhs)
| Overloaded in-equality comparison operator, allows the user to compare the value of two SmartPtrs.
template<class U1 , class U2 >
bool | operator!= (const SmartPtr< U1 > &lhs, U2 *raw_rhs)
| Overloaded in-equality comparison operator, allows the user to compare the value of a SmartPtr with a raw pointer.
template<class U1 , class U2 >
bool | operator!= (U1 *lhs, const SmartPtr< U2 > &raw_rhs)
| Overloaded in-equality comparison operator, allows the user to compare the value of a SmartPtr with a raw pointer.

## Detailed Description

### template<class T>
class Coin::SmartPtr< T >

Template class for Smart Pointers.

A SmartPtr behaves much like a raw pointer, but manages the lifetime of an object, deleting the object automatically. This class implements a reference-counting, intrusive smart pointer design, where all objects pointed to must inherit off of ReferencedObject, which stores the reference count. Although this is intrusive (native types and externally authored classes require wrappers to be referenced by smart pointers), it is a safer design. A more detailed discussion of these issues follows after the usage information.

Usage Example: Note: to use the SmartPtr, all objects to which you point MUST inherit off of ReferencedObject.

         *
         * In MyClass.hpp...
         *
         * #include "CoinSmartPtr.hpp"
         *
         *  class MyClass : public Coin::ReferencedObject // must derive from ReferencedObject
         *    {
         *      ...
         *    }
         *
         * In my_usage.cpp...
         *
         * #include "CoinSmartPtr.hpp"
         * #include "MyClass.hpp"
         *
         * void func(AnyObject& obj)
         *  {
         *    SmartPtr<MyClass> ptr_to_myclass = new MyClass(...);
         *    // ptr_to_myclass now points to a new MyClass,
         *    // and the reference count is 1
         *
         *    ...
         *
         *    obj.SetMyClass(ptr_to_myclass);
         *    // Here, let's assume that AnyObject uses a
         *    // SmartPtr<MyClass> internally here.
         *    // Now, both ptr_to_myclass and the internal
         *    // SmartPtr in obj point to the same MyClass object
         *    // and its reference count is 2.
         *
         *    ...
         *
         *    // No need to delete ptr_to_myclass, this
         *    // will be done automatically when the
         *    // reference count drops to zero.
         *
         *  }
         *
         *

It is not necessary to use SmartPtr's in all cases where an object is used that has been allocated "into" a SmartPtr. It is possible to just pass objects by reference or regular pointers, even if lower down in the stack a SmartPtr is to be held on to. Everything should work fine as long as a pointer created by "new" is immediately passed into a SmartPtr, and if SmartPtr's are used to hold on to objects.

Other Notes: The SmartPtr implements both dereference operators -> & *. The SmartPtr does NOT implement a conversion operator to the raw pointer. Use the GetRawPtr() method when this is necessary. Make sure that the raw pointer is NOT deleted. The SmartPtr implements the comparison operators == & != for a variety of types. Use these instead of

         *    if (GetRawPtr(smrt_ptr) == ptr) // Don't use this
         *

SmartPtr's, as currently implemented, do NOT handle circular references. For example: consider a higher level object using SmartPtrs to point to A and B, but A and B also point to each other (i.e. A has a SmartPtr to B and B has a SmartPtr to A). In this scenario, when the higher level object is finished with A and B, their reference counts will never drop to zero (since they reference each other) and they will not be deleted. This can be detected by memory leak tools like valgrind. If the circular reference is necessary, the problem can be overcome by a number of techniques:

1) A and B can have a method that "releases" each other, that is they set their internal SmartPtrs to NULL.

         *        void AClass::ReleaseCircularReferences()
         *          {
         *          smart_ptr_to_B = NULL;
         *          }
         *

Then, the higher level class can call these methods before it is done using A & B.

2) Raw pointers can be used in A and B to reference each other. Here, an implicit assumption is made that the lifetime is controlled by the higher level object and that A and B will both exist in a controlled manner. Although this seems dangerous, in many situations, this type of referencing is very controlled and this is reasonably safe.

3) This SmartPtr class could be redesigned with the Weak/Strong design concept. Here, the SmartPtr is identified as being Strong (controls lifetime of the object) or Weak (merely referencing the object). The Strong SmartPtr increments (and decrements) the reference count in ReferencedObject but the Weak SmartPtr does not. In the example above, the higher level object would have Strong SmartPtrs to A and B, but A and B would have Weak SmartPtrs to each other. Then, when the higher level object was done with A and B, they would be deleted. The Weak SmartPtrs in A and B would not decrement the reference count and would, of course, not delete the object. This idea is very similar to item (2), where it is implied that the sequence of events is controlled such that A and B will not call anything using their pointers following the higher level delete (i.e. in their destructors!). This is somehow safer, however, because code can be written (however expensive) to perform run-time detection of this situation. For example, the ReferencedObject could store pointers to all Weak SmartPtrs that are referencing it and, in its destructor, tell these pointers that it is dying. They could then set themselves to NULL, or set an internal flag to detect usage past this point.

Comments on Non-Intrusive Design: In a non-intrusive design, the reference count is stored somewhere other than the object being referenced. This means, unless the reference counting pointer is the first referencer, it must get a pointer to the referenced object from another smart pointer (so it has access to the reference count location). In this non-intrusive design, if we are pointing to an object with a smart pointer (or a number of smart pointers), and we then give another smart pointer the address through a RAW pointer, we will have two independent, AND INCORRECT, reference counts. To avoid this pitfall, we use an intrusive reference counting technique where the reference count is stored in the object being referenced.

Definition at line 319 of file CoinSmartPtr.hpp.

## Constructor & Destructor Documentation

template<class T>

Coin::SmartPtr< T >::SmartPtr | ( |  | ) | `[inline]`

Default constructor, initialized to NULL.

Definition at line 384 of file CoinSmartPtr.hpp.

template<class T>

Coin::SmartPtr< T >::SmartPtr | ( | const SmartPtr< T > & | copy | ) | `[inline]`

Copy constructor, initialized from copy.

Definition at line 387 of file CoinSmartPtr.hpp.

template<class T>

Coin::SmartPtr< T >::SmartPtr | ( | T * | ptr | ) | `[inline]`

Constructor, initialized from T* ptr.

Definition at line 392 of file CoinSmartPtr.hpp.

template<class T>

Coin::SmartPtr< T >::~SmartPtr | ( |  | ) | `[inline]`

Destructor, automatically decrements the reference count, deletes the object if necessary.

Definition at line 398 of file CoinSmartPtr.hpp.

## Member Function Documentation

template<class T>

T* Coin::SmartPtr< T >::GetRawPtr | ( |  | ) | const`[inline]`

Returns the raw pointer contained.

Use to get the value of the raw ptr (i.e. to pass to other methods/functions, etc.) Note: This method does NOT copy, therefore, modifications using this value modify the underlying object contained by the SmartPtr, NEVER delete this returned value.

Definition at line 327 of file CoinSmartPtr.hpp.

template<class T>

bool Coin::SmartPtr< T >::IsValid | ( |  | ) | const`[inline]`

Returns true if the SmartPtr is NOT NULL.

Use this to check if the SmartPtr is not null This is preferred to if(GetRawPtr(sp) != NULL)

Definition at line 333 of file CoinSmartPtr.hpp.

template<class T>

bool Coin::SmartPtr< T >::IsNull | ( |  | ) | const`[inline]`

Returns true if the SmartPtr is NULL.

Use this to check if the SmartPtr IsNull. This is preferred to if(GetRawPtr(sp) == NULL)

Definition at line 339 of file CoinSmartPtr.hpp.

template<class T>

void Coin::SmartPtr< T >::ReleasePointer_ | ( |  | ) | `[inline, private]`

Release the currently referenced object.

Definition at line 348 of file CoinSmartPtr.hpp.

template<class T>

SmartPtr<T>& Coin::SmartPtr< T >::SetFromRawPtr_ | ( | T * | rhs | ) | `[inline, private]`

Set the value of the internal raw pointer from another raw pointer, releasing the previously referenced object if necessary.

Definition at line 360 of file CoinSmartPtr.hpp.

template<class T>

SmartPtr<T>& Coin::SmartPtr< T >::SetFromSmartPtr_ | ( | const SmartPtr< T > & | rhs | ) | `[inline, private]`

Set the value of the internal raw pointer from a SmartPtr, releasing the previously referenced object if necessary.

Definition at line 371 of file CoinSmartPtr.hpp.

template<class T>

T* Coin::SmartPtr< T >::operator-> | ( |  | ) | const`[inline]`

Overloaded arrow operator, allows the user to call methods using the contained pointer.

Definition at line 407 of file CoinSmartPtr.hpp.

template<class T>

T& Coin::SmartPtr< T >::operator* | ( |  | ) | const`[inline]`

Overloaded dereference operator, allows the user to dereference the contained pointer.

Definition at line 416 of file CoinSmartPtr.hpp.

template<class T>

SmartPtr<T>& Coin::SmartPtr< T >::operator= | ( | T * | rhs | ) | `[inline]`

Overloaded equals operator, allows the user to set the value of the SmartPtr from a raw pointer.

Definition at line 425 of file CoinSmartPtr.hpp.

template<class T>

SmartPtr<T>& Coin::SmartPtr< T >::operator= | ( | const SmartPtr< T > & | rhs | ) | `[inline]`

Overloaded equals operator, allows the user to set the value of the SmartPtr from another SmartPtr.

Definition at line 432 of file CoinSmartPtr.hpp.

## Friends And Related Function Documentation

template<class T>
template<class U1 , class U2 >

bool operator== | ( | const SmartPtr< U1 > & | lhs,
|  | const SmartPtr< U2 > & | rhs |
| ) |  |  | `[friend]`

Overloaded equality comparison operator, allows the user to compare the value of two SmartPtrs.

template<class T>
template<class U1 , class U2 >

bool operator== | ( | const SmartPtr< U1 > & | lhs,
|  | U2 * | raw_rhs |
| ) |  |  | `[friend]`

Overloaded equality comparison operator, allows the user to compare the value of a SmartPtr with a raw pointer.

template<class T>
template<class U1 , class U2 >

bool operator== | ( | U1 * | lhs,
|  | const SmartPtr< U2 > & | raw_rhs |
| ) |  |  | `[friend]`

Overloaded equality comparison operator, allows the user to compare the value of a raw pointer with a SmartPtr.

template<class T>
template<class U1 , class U2 >

bool operator!= | ( | const SmartPtr< U1 > & | lhs,
|  | const SmartPtr< U2 > & | rhs |
| ) |  |  | `[friend]`

Overloaded in-equality comparison operator, allows the user to compare the value of two SmartPtrs.

template<class T>
template<class U1 , class U2 >

bool operator!= | ( | const SmartPtr< U1 > & | lhs,
|  | U2 * | raw_rhs |
| ) |  |  | `[friend]`

Overloaded in-equality comparison operator, allows the user to compare the value of a SmartPtr with a raw pointer.

template<class T>
template<class U1 , class U2 >

bool operator!= | ( | U1 * | lhs,
|  | const SmartPtr< U2 > & | raw_rhs |
| ) |  |  | `[friend]`

Overloaded in-equality comparison operator, allows the user to compare the value of a SmartPtr with a raw pointer.

## Member Data Documentation

template<class T>

T* Coin::SmartPtr< T >::ptr_`[private]`

Actual raw pointer to the object.

Definition at line 345 of file CoinSmartPtr.hpp.

The documentation for this class was generated from the following file:

- /home/coin/svn-release/Alps-1.5.2/CoinUtils/src/CoinSmartPtr.hpp