PtrHolder.h

Classes

PtrHolder -- Hold and delete pointers not deleted by object destructors (full description)

template<class T> class PtrHolder

Interface

Public Members

PtrHolder()

PtrHolder(T *pointer, Bool isCArray = False)

~PtrHolder()

void set(T *pointer, Bool isCarray = False, Bool deleteCurrentPtr = True)

void clear(Bool deleteCurrentPtr = True)

T *ptr()

const T *ptr() const

Bool isCArray() const

Private Members

PtrHolder(const PtrHolder<T> &other)

PtrHolder<T> &operator=(const PtrHolder<T> &other)

void delete_pointer_if_necessary()

Description

Review Status

Reviewed By:

troberts

Date Reviewed:

1995/07/29

Programs:

Tests:

tPtrHolder

Prerequisite

module Exceptions

Synopsis

PtrHolders hold allocated pointers which should be deleted when an exception is thrown. Exceptions only call destructors of objects. Thus, for example, storage allocated in a global function (outside of an object)is not deleted. A PtrHolder solves this problem: it merely holds the pointer and deletes it when it is destroyed itself, e.g. when an exception is thrown or when the function exits normally.

Example

    void func(Int *ptr); // some other function that takes a pointer
    // ...
    // True below means it's an array, False (the default) would mean
    // a singleton object.
    PtrHolder<Int> iholder(new Int[10000], True);
    func(iholder);                           // converts automatically to ptr
    (iholder.ptr() + 5) = 11;                // use pointer explicitly
    some_function_that_throws_exception();   // pointer is deleted

Motivation

Avoid leaks when throwing/catching exceptions.

To Do

Use the autoptr class from the Standard Library

Member Description

PtrHolder()

The default constructor uses a null pointer.

PtrHolder(T *pointer, Bool isCArray = False)

Construct a PtrHolder from a pointer which MUST have been allocated from new, since the destructor will call delete on it. If the pointer is to an array, i.e. allocated with operator new[], then isCarray should be set to True. (This parameter is required because C-arrays need to be deleted with delete[].)

After the pointer is placed into the holder, the user should not manually delete the pointer; the PtrHolder object will do that, unless set() or clear() is called with deleteCurrentPtr set to False. The pointer must also only be put into one holder to avoid double deletion.

~PtrHolder()

void set(T *pointer, Bool isCarray = False, Bool deleteCurrentPtr = True)

Set the pointer to a new value. If deleteCurrentPtr is True (the default), then delete the existing pointer first. If isCarray is True, then the new pointer is assumed to have been allocated with new[].

void clear(Bool deleteCurrentPtr = True)

Set the current pointer to null; if deletePtr is True (the default), then the current pointer is deleted first.

T ptr()
const T ptr() const

Attempt to automatically release a pointer when required. If the compiler can't figure it out, you can use the ptr() member function directly.