delete有误

ghostgorst

#include<new> #include<stdlib.h> #include <stdio.h> using namespace std; class object { public: &nbsp;&nbsp;&nbsp;&nbsp;int x; &nbsp;&nbsp;&nbsp;&nbsp;object():x(4){ } }; const int iObjNum = 10; int main(int argc, char * argv[]) { &nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;char * ptr = (char*) malloc(iObjNum*sizeof(object)); &nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;object *pObj[iObjNum];&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;for(int i=0; i<iObjNum; ++i) &nbsp;&nbsp;&nbsp;&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;pObj[i]=new (ptr+i*sizeof(object)) object;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;for (int j=0; j<iObjNum; ++j) &nbsp;&nbsp;&nbsp;&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;delete pObj[j]; &nbsp;&nbsp;&nbsp;&nbsp;}    &nbsp;&nbsp;&nbsp;&nbsp;return 0; }

谁能告诉我正确用法么?

[ 本帖最后由 ghostgorst 于 2009-8-7 18:29 编辑 ]

OwnWaterloo

for(int i=0; i<iObjNum; ++i)
    {
        pObj[i ]=new (ptr+i*sizeof(object)) object;        
    }

这行代码中的new，并没有分配内存。 仅仅是在一个内存地址上“构造出”对象。


真正分配内存的代码在这里：
    char * ptr = (char*) malloc(iObjNum*sizeof(object));



与之搭配的行为是：
    for (int j=0; j<iObjNum; ++j)
    {
        pObj[i ]->~object(); // 调用析构函数， 销毁对象
    }

    free(ptr);  // 释放内存。

syncpk99

直接调用object的析构函数，然后在free ptr

ghostgorst

D:\Program Files\Microsoft Visual Studio\VC98\Include\NEW


#ifndef __PLACEMENT_NEW_INLINE
#define __PLACEMENT_NEW_INLINE
inline void *__cdecl operator new(size_t, void *_P)
        {return (_P); }
#if     _MSC_VER >= 1200
inline void __cdecl operator delete(void *, void *)
        {return; }
#endif
#endif

我就是想弄明白这对new/delete用法

bruceteen

呵呵，malloc出来的东西用delete释放
并且，一次malloc的东西，用delete分批释放

ghostgorst

#include<new>
#include<stdlib.h>
#include <stdio.h>
using namespace std;
class object
{
public:
        int x;
        object()(4){ }
};
const int iObjNum = 10;
int main(int argc, char * argv[])
{
       
    char * ptr = new char[iObjNum*sizeof(object)];
   
        object *pObj[iObjNum];       
    for(int i=0; i<iObjNum; ++i)
    {
        pObj=new (ptr+i*sizeof(object)) object;               
    }
    for (int j=0; j<iObjNum; ++j)
    {
        delete pObj[j];
    }  
       
    return 0;
}


这样也还是出错啊

OwnWaterloo

google "placement new"

aaaaa5aa

这里为什么不用构造函数和析构函数

dtimes6

#include<new> #include<stdlib.h> #include <stdio.h> using namespace std; class object { public:         int x;         object():x(4){}         void* operator new( size_t sz, void* p) { return p; }         void operator delete( void* p) {} }; const int iObjNum = 10; int main(int argc, char * argv[]) {              char * ptr = new char[iObjNum*sizeof(object)];              object *pObj[iObjNum];             for(int i=0; i<iObjNum; ++i)     {         pObj[i]=new (ptr+i*sizeof(object)) object;                    }     for (int j=0; j<iObjNum; ++j)     {         delete pObj[j];     }       delete [] ptr;     return 0; }

[ 本帖最后由 dtimes6 于 2009-8-8 15:57 编辑 ]

starwing83

#include<new> #include<stdlib.h> #include <stdio.h> using namespace std; class object { public: &nbsp;&nbsp;&nbsp;&nbsp;int x; &nbsp;&nbsp;&nbsp;&nbsp;object(): x(4) { } }; const int iObjNum = 10; int main(int argc, char * argv[]) { &nbsp;&nbsp;&nbsp;&nbsp;char * ptr = (char*) malloc(iObjNum * sizeof(object)); &nbsp;&nbsp;&nbsp;&nbsp;object *pObj[iObjNum]; &nbsp;&nbsp;&nbsp;&nbsp;for (int i = 0; i < iObjNum; ++i) &nbsp;&nbsp;&nbsp;&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;pObj[i] = new(ptr + i*sizeof(object)) object; &nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;for (int j = 0; j < iObjNum; ++j) &nbsp;&nbsp;&nbsp;&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;pObj[j]->~object(); &nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;free(ptr); &nbsp;&nbsp;&nbsp;&nbsp;return 0; }

[ 本帖最后由 starwing83 于 2009-8-8 12:24 编辑 ]