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icptrholder.h

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/* -*- Mode: C++ -*- */

/**
 * @file    icptrholder.h
 * @author  wyau (08/29/02)
 * @brief   C++ template classes for managing C++ pointers returned by VComponent::get_..._component, 
 *          VComponent::get_..._property, ICalPropety::get_..._value.
 * @remarks VComponent::get... functions returns a C++ oject that wraps the libical implementation.
 *          It is important to note that the wrapped implementation still belongs to the orginal
 *          component. To stop memory leak, caller must delete the pointer. However, the destructor
 *          will call the appropriate free function. eg. ~VComponent calls icalcomponent_free(imp).
 *          As stated previously, imp stil belongs to the original component. To avoid freeing the
 *          wrapped "imp", caller must set the "imp" to null before deleting the pointer.
 *
 *          The template class relieves the burden of memory management when used as a stack based
 *          object. The class holds a pointer to the C++ Wrapper. The destructor set the imp to
 *          null before deleting the pointer.
 *
 *          Each C++ Wrapper instantiates a template class in it's corresponding .h file.
 *
 *          Usage example:
 *             VComponentTmpPtr p;   // VComponentTmpPtr is an instantiation of this template
 *             for (p=component.get_first_component; p!= NULL; p=component.get_next_component) {
 *
 * (C) COPYRIGHT 2001, Critical Path

 This program is free software; you can redistribute it and/or modify
 it under the terms of either: 

    The LGPL as published by the Free Software Foundation, version
    2.1, available at: http://www.fsf.org/copyleft/lesser.html

  Or:

    The Mozilla Public License Version 1.0. You may obtain a copy of
    the License at http://www.mozilla.org/MPL/
 */

#ifndef __ICPTRHOLDER_H__
#define __ICPTRHOLDER_H__

template<class T> class ICPointerHolder {
public:
    ICPointerHolder() { ptr = NULL; }
    ICPointerHolder(T* p) { ptr = p; }

    // copy constructor to support assignment
    ICPointerHolder(const ICPointerHolder& ip) {
        ptr = ip.ptr;

        // We need to transfer ownership of ptr to this object by setting
        // ip's ptr to null. Otherwise, ptr will de deleted twice.
        // const ugliness requires us to do the const_cast.
        ICPointerHolder *ipp = const_cast<ICPointerHolder*>(&ip);
        ipp->ptr = NULL;
    };

   ~ICPointerHolder() {
        release();
    }

    ICPointerHolder& operator=(T* p) {
        this->release();
        ptr = p;
        return *this;
    }

    ICPointerHolder& operator=(ICPointerHolder& p) {
        this->release();
        ptr = p.ptr;            // this transfer ownership of the pointer
        p.ptr = NULL;           // set it to null so the pointer won't get delete twice.
        return *this;
    }

    int operator!=(T* p) {return (ptr != p);}
    int operator==(T* p) {return (ptr == p);}

    operator T*() const {
        return ptr;
    }

    T* operator->() const {
        assert(ptr);
        return ptr;
    }

    T& operator*() {
        assert(ptr);
        return *ptr;
    }

private:
    void  release() {
        if (ptr != NULL) {
            ptr->detach();
            delete ptr;
            ptr = NULL;
        }
    }

    T*    ptr;
};

#endif

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