delete问题

[zw1987122]

class ScrPtr {
friend class ScreenPtr;
Screen *sp;
size_t use;
ScrPtr(Screen *p): sp(p), use(1) { }
~ScrPtr() { delete sp; }
};
这是C++ Primer书上的，为什么sp没new就可以delete

[fuyifan]

sp不是该类new的，此外即使sp=NULL也是可以delete的

[pengzhixi]

class ScreenPtr;//你贴下这个类的定义

[十八道胡同]

[Quote=引用楼主 zw1987122 的回复:]
class ScrPtr {
friend class ScreenPtr;
Screen *sp;
size_t use;
ScrPtr(Screen *p): sp(p), use(1) { }
~ScrPtr() { delete sp; }
};
这是C++ Primer书上的，为什么sp没new就可以delete
[/Quote]
这个只是声明，具体的实现里面会new

[hahalxp]

空指针也可以delete的
删除空指针是安全的(因为它什么也没做)。所以，在写构造函数，赋值操作符，或其他成员函数时，类的每个指针成员要么指向有效的内存，要么就指向空，那在你的析构函数里你就可以只用简单地delete掉他们，而不用担心他们是不是被new过。

[赵4老师]

c:\Microsoft SDK\src\crt\delete.cpp

/***
*delete.cpp - defines C++ scalar delete routine, non-debug version
*
*       Copyright (c) 1990-2001, Microsoft Corporation.  All rights reserved.
*
*Purpose:
*       Defines C++ delete routine.
*
*******************************************************************************/

#ifndef _DEBUG

#include <cruntime.h>
#include <malloc.h>
#include <new.h>
#include <windows.h>
#include <rtcsup.h>

void operator delete( void * p )
{
    RTCCALLBACK(_RTC_Free_hook, (p, 0));

    free( p );
}

#endif  /* _DEBUG */

c:\Microsoft SDK\src\crt\free.c

/***
*free.c - free an entry in the heap
*
*       Copyright (c) 1989-2001, Microsoft Corporation. All rights reserved.
*
*Purpose:
*       Defines the following functions:
*           free()     - free a memory block in the heap
*
*******************************************************************************/

#ifdef WINHEAP

#include <cruntime.h>
#include <malloc.h>
#include <winheap.h>
#include <windows.h>
#include <internal.h>
#include <mtdll.h>
#include <dbgint.h>
#include <rtcsup.h>

/***
*void free(pblock) - free a block in the heap
*
*Purpose:
*       Free a memory block in the heap.
*
*       Special ANSI Requirements:
*
*       (1) free(NULL) is benign.
*
*Entry:
*       void *pblock - pointer to a memory block in the heap
*
*Return:
*       <void>
*
*******************************************************************************/

void __cdecl _free_base (void * pBlock)
{


        if (pBlock == NULL)
            return;

        RTCCALLBACK(_RTC_Free_hook, (pBlock, 0));

#ifndef _WIN64
        if ( __active_heap == __V6_HEAP )
        {
            PHEADER     pHeader;

#ifdef _MT
            _mlock( _HEAP_LOCK );
            __try {
#endif  /* _MT */

            if ((pHeader = __sbh_find_block(pBlock)) != NULL)
                __sbh_free_block(pHeader, pBlock);

#ifdef _MT
            }
            __finally {
                _munlock( _HEAP_LOCK );
            }
#endif  /* _MT */

            if (pHeader == NULL)
                HeapFree(_crtheap, 0, pBlock);
        }
#ifdef CRTDLL
        else if ( __active_heap == __V5_HEAP )
        {
            __old_sbh_region_t *preg;
            __old_sbh_page_t *  ppage;
            __old_page_map_t *  pmap;
#ifdef _MT
            _mlock(_HEAP_LOCK );
            __try {
#endif  /* _MT */

            if ( (pmap = __old_sbh_find_block(pBlock, &preg, &ppage)) != NULL )
                __old_sbh_free_block(preg, ppage, pmap);

#ifdef _MT
            }
            __finally {
                _munlock(_HEAP_LOCK );
            }
#endif  /* _MT */

            if (pmap == NULL)
                HeapFree(_crtheap, 0, pBlock);
        }
#endif  /* CRTDLL */
        else    //  __active_heap == __SYSTEM_HEAP
#endif  /* _WIN64 */
        {
            HeapFree(_crtheap, 0, pBlock);
        }
}


#else  /* WINHEAP */


#include <cruntime.h>
#include <heap.h>
#include <malloc.h>
#include <mtdll.h>
#include <stdlib.h>
#include <dbgint.h>

/***
*void free(pblock) - free a block in the heap
*
*Purpose:
*       Free a memory block in the heap.
*
*       Special Notes For Multi-thread: The non-multi-thread version is renamed
*       to _free_lk(). The multi-thread free() simply locks the heap, calls
*       _free_lk(), then unlocks the heap and returns.
*
*Entry:
*       void *pblock - pointer to a memory block in the heap
*
*Return:
*       <void>
*
*******************************************************************************/

#ifdef _MT

void __cdecl _free_base (
        void *pblock
        )
{
       /* lock the heap
        */
        _mlock(_HEAP_LOCK);

        /* free the block
         */
        _free_base_lk(pblock);

        /* unlock the heap
         */
        _munlock(_HEAP_LOCK);
}


/***
*void _free_lk(pblock) - non-locking form of free
*
*Purpose:
*       Same as free() except that no locking is performed
*
*Entry:
*       See free
*
*Return:
*
*******************************************************************************/

void __cdecl _free_base_lk (

#else  /* _MT */

void __cdecl _free_base (

#endif  /* _MT */

        REG1 void *pblock
        )
{
        REG2 _PBLKDESC pdesc;


        /*
         * If the pointer is NULL, just return [ANSI].
         */

        if (pblock == NULL)
            return;

        /*
         * Point to block header and get the pointer back to the heap desc.
         */

        pblock = (char *)pblock - _HDRSIZE;
        pdesc = *(_PBLKDESC*)pblock;

        /*
         * Validate the back pointer.
         */

        if (_ADDRESS(pdesc) != pblock)
            _heap_abort();

        /*
         * Pointer is ok.  Mark block free.
         */

        _SET_FREE(pdesc);

        /*
         * Check for special conditions under which the rover is reset.
         */
        if ( (_heap_resetsize != 0xffffffff) &&
             (_heap_desc.proverdesc->pblock > pdesc->pblock) &&
             (_BLKSIZE(pdesc) >= _heap_resetsize) )
        {
            _heap_desc.proverdesc = pdesc;
        }
        else if ( _heap_desc.proverdesc == pdesc->pnextdesc )
        {
            _heap_desc.proverdesc = pdesc;
        }
}

#endif  /* WINHEAP */

[only_delusion]

应该是前边有new 你的这个是有别的类嵌套进来了....你应该看全点...... 一般的只有NEW才配有delete
没有new delete没有意义的.........