为什么编译器不会“p = NULL”程序后自动执行“删除p”？ [英] Why compilers do not "p = NULL" automatically after programs do "delete p"?

问题描述

我们都知道以下代码是危险的：

{

int * p = new int;

删除p;

删除p;

}

我们也知道如果p == NULL，编译器不会删除p 。


那么为什么编译器不会p = NULL程序后自动删除p？

Hi,
We all know the below codes are dangerous:
{
int *p = new int;
delete p;
delete p;
}
And we also know the compilers do not delete p if p==NULL.

So why compilers do not "p = NULL" automatically after programs do "delete p"?

推荐答案

>那么为什么编译器不会p = NULL在>程序之后自动执行删除p？


因为他们不能。您将不得不以某种方式将p的地址传递给

将p设置为NULL。当然这只是它的一个方面。

>So why compilers do not "p = NULL" automatically after >programs do "delete p"?

Because they can''t. You will have to pass somehow the address of p to
set p to NULL. Of course this is just one aspect of it.

gary写道：

gary wrote:

我们都知道下面的代码是危险的：
{
int * p = new int;
删除p;
删除p;
}
那么为什么编译器不会p = NULL。程序后自动执行删除p？

Hi,
We all know the below codes are dangerous:
{
int *p = new int;
delete p;
delete p;
}
And we also know the compilers do not delete p if p==NULL.

So why compilers do not "p = NULL" automatically after programs do "delete p"?

一个问题就是效率。 ''p = NULL''至少需要一条指令

才能完成。如果你在一个非常深的循环中删除一个点，那么成本可能会很大。


南

One problem is efficiency. ''p = NULL'' at least takes one instruction
to complete. If you delete a point in a very deep loop, the cost could
be huge.

Nan

gary< zw ** @ gawab.com>写道：

gary <zw**@gawab.com> wrote:

我们都知道下面的代码是危险的：
{* / int int * p = new int;
delete p;
delete p;
}
我们也知道如果p == NULL，编译器不会删除p。

那么为什么编译器不会p = NULL程序后自动执行删除p？

Hi,
We all know the below codes are dangerous:
{
int *p = new int;
delete p;
delete p;
}
And we also know the compilers do not delete p if p==NULL.

So why compilers do not "p = NULL" automatically after programs do "delete p"?

Stroustrup在他的FAQ中回答这个问题：
http://www.research.att.com/~bs/bs_f...ml#delete-zero


-

Marcus Kwok

Stroustrup answers this in his FAQ:
http://www.research.att.com/~bs/bs_f...ml#delete-zero

--
Marcus Kwok

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