我做了個試驗，試驗條件是XP + VS 2005，在Release版本下測試，結果相當令人吃驚。

malloc版本：

#define ITEM_TIMES 1000000

#include <malloc.h>

#define NULL 0

typedef struct UPDATE_ITEM
{
bool down_succeeded;
} *UPDATE_ITEM_PTR;

typedef struct DOWN_ITEM
{
UPDATE_ITEM_PTR update_item;
bool pack;

DOWN_ITEM* next;
} *DOWN_ITEM_PTR;

DOWN_ITEM_PTR create_down_item(bool pack, bool down_succeeded)
{
DOWN_ITEM_PTR down_item = (DOWN_ITEM_PTR) malloc(sizeof(DOWN_ITEM));
down_item->pack = pack;

down_item->update_item = (UPDATE_ITEM_PTR) malloc(sizeof(UPDATE_ITEM));
down_item->update_item->down_succeeded = down_succeeded;

down_item->next = NULL;

return down_item;
}

void free_all_down_item(DOWN_ITEM_PTR root_down_item)
{
DOWN_ITEM_PTR down_item_ptr = root_down_item;

while(down_item_ptr)
{
if(down_item_ptr->update_item)
free(down_item_ptr->update_item);

DOWN_ITEM_PTR temp_ptr = down_item_ptr;
down_item_ptr = down_item_ptr->next;

free(temp_ptr);
}
}

int main()
{
DOWN_ITEM_PTR first, last, ptr;

for(int i = 0; i < ITEM_TIMES; i++)
{
if(i == 0)
{
first = create_down_item(true, false);
last = first;
}
else
{
ptr = create_down_item(true, false);
last->next = ptr;

last = ptr;
}
}

while(1)
;

free_all_down_item(first);

return 0;
}

vector版本：

#include <vector>

using namespace std;

typedef struct UPADTE_ITEM
{
bool down_succeeded;

UPADTE_ITEM()
{
down_succeeded = false;
}
} *UPADTE_ITEM_PTR;

typedef struct DOWN_ITEM
{
UPADTE_ITEM_PTR update_item;
bool pack;

DOWN_ITEM()
{
update_item = NULL;
pack = false;
}

DOWN_ITEM(UPADTE_ITEM_PTR _update_item, bool _pack)
{
update_item = _update_item;
pack = _pack;
}
} *DOWN_ITEM_PTR;

int main()
{
vector<DOWN_ITEM> down_item_vec;

UPADTE_ITEM_PTR update_item_list = new UPADTE_ITEM[ITEM_TIMES];

for(int i = 0; i < ITEM_TIMES; i++)
down_item_vec.push_back(DOWN_ITEM(&update_item_list[i], true));

while(1)
;

delete[] update_item_list;

return 0;
}

改變ITEM_TIMES的值以改變迭代次數。

內存消耗比較：

迭代1000次: malloc - 868k vector - 796K
迭代10000次 : malloc - 1784k vector - 916k
迭代100000次 : malloc - 10956k vector - 2000k
迭代1000000次 : malloc - 102648k vector - 10008k

vector版本內存消耗更少，我想應該是多次malloc導致內存消耗劇增，而vector只在必要的時候才重新分配內存。
而malloc版本在代碼中所涉及的指針操作也相當煩瑣。
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