GetPointer
GetPointer
该函数返回对象指针.
void* GetPointer(
any_class anyobject // object of any class
);参数
- anyobject
[in] 任何类的对象。
返回值
该函数返回对象指针。
注意
只有类对象才有指针。结构和简单类型变量没有指针。使用 new() 运算符创建但未创建的类对象仍然有指针，但这种指针属于自动类型 POINTER_AUTOMATIC，因此无法应用 delete() 运算符。此外，类型指针与 POINTER_AUTOMATIC 类型的动态指针相同。
由于结构类型和简单类型的变量没有指针，因此禁止将 GetPointer() 函数应用于它们。也将禁止将指针作为函数参数传递。在所有这些情况下，编译器都会发出错误提示。
尝试使用错误的指针会导致程序关键终止。因此，在使用指针之前应调用CheckPointer()函数。以下情况下的指针可能是错误的：
该函数可用于检查指针的有效性。非零值保证指针可用于访问。
示例：
//+------------------------------------------------------------------+
//| Check_GetPointer.mq5 |
//| Copyright 2009, MetaQuotes Software Corp. |
//| https://www.mql5.com |
//+------------------------------------------------------------------+
#property copyright "2009, MetaQuotes Software Corp."
#property link "https://www.mql5.com"
#property version "1.00"
//+------------------------------------------------------------------+
//| Class implementing the list element |
//+------------------------------------------------------------------+
class CItem
{
int m_id;
string m_comment;
CItem* m_next;
public:
CItem() { m_id=0; m_comment=NULL; m_next=NULL; }
~CItem() { Print("Destructor of ",m_id,
(CheckPointer(GetPointer(this))==POINTER_DYNAMIC)?
"dynamic":"non-dynamic"); }
void Initialize(int id,string comm) { m_id=id; m_comment=comm; }
void PrintMe() { Print(__FUNCTION__,":",m_id,m_comment); }
int Identifier() { return(m_id); }
CItem* Next() {return(m_next); }
void Next(CItem *item) { m_next=item; }
};
//+------------------------------------------------------------------+
//| Simplest class of the list |
//+------------------------------------------------------------------+
class CMyList
{
CItem* m_items;
public:
CMyList() { m_items=NULL; }
~CMyList() { Destroy(); }
bool InsertToBegin(CItem* item);
void Destroy();
};
//+------------------------------------------------------------------+
//| Inserts list element at the beginning |
//+------------------------------------------------------------------+
bool CMyList::InsertToBegin(CItem* item)
{
if(CheckPointer(item)==POINTER_INVALID) return(false);
//---
item.Next(m_items);
m_items=item;
//---
return(true);
}
//+------------------------------------------------------------------+
//| Deletes the list by deleting elements |
//+------------------------------------------------------------------+
void CMyList::Destroy()
{
//--- service pointer to work in a loop
CItem* item;
//--- go through the loop and try to delete dynamic pointers
while(CheckPointer(m_items)!=POINTER_INVALID)
{
item=m_items;
m_items=m_items.Next();
if(CheckPointer(item)==POINTER_DYNAMIC)
{
Print("Dynamyc object ",item.Identifier()," to be deleted");
delete (item);
}
else Print("Non-dynamic object ",item.Identifier()," cannot be deleted");
}
//---
}
//+------------------------------------------------------------------+
//| Script program start function |
//+------------------------------------------------------------------+
void OnStart()
{
CMyList list;
CItem items[10];
CItem* item;
//--- create and add into the list a dynamic object pointer
item=new CItem;
if(item!=NULL)
{
item.Initialize(100,"dynamic");
item.PrintMe();
list.InsertToBegin(item);
}
//--- add automatic pointers into the list
for(int i=0; i<10; i++)
{
items[i].Initialize(i,"automatic");
items[i].PrintMe();
item=GetPointer(items[i]);
if(CheckPointer(item)!=POINTER_INVALID)
list.InsertToBegin(item);
}
//--- add one more dynamic object pointer at the list beginning
item=new CItem;
if(item!=NULL)
{
item.Initialize(200,"dynamic");
item.PrintMe();
list.InsertToBegin(item);
}
//--- delete all the list elements
list.Destroy();
//--- all the list elements will be deleted after the script is over
//--- see the Experts tab in the terminal
}另请参阅
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