C ++ - 为什么删除后将对象设置为null？ [英] C++ - Why set object to null after deleting?

问题描述

我在网上找到下面的链接列表代码：

I am looking at the following piece of linked list code I found online:

void DeleteAfter(Node **head){
      if(*head==NULL){
            return;
      }else{
            Node *temp = NULL;
            temp = (*head)->next;
            (*head)->next = (*head)->next->next;
            delete temp;
            temp=NULL;
      }
}

我不是那么熟练的C ++，是一个坏问题，但为什么temp被设置为NULL后删除？这是必要的步骤吗？

I am not that skilled with C++, so this could be a bad question, but why is temp being set to NULL after being deleted? Is this a necessary step?

推荐答案

这是不必要的。有些人养成这样做的习惯，即使没有结果。一个积极的编译器优化器将消除这个代码，所以它实际上没有任何危害。但我会写：

It's unnecessary. Some people make a habit of doing this even when it has no result. An aggressive compiler optimizer will eliminate this code, so it doesn't actually do any harm. But I would have written:

void DeleteAfter(Node *head) {
  if (head) {
    Node *next = head->next;
    if (next) {
      head->next = next->next;
      delete next;
    }
  }
}

注意我删除了无用的级别的间接，并添加了一个检查，以确保有一个节点之后删除。

Note I eliminated a useless level of indirection and added a check to make sure there's a "node after" to delete.

习惯的基本原理是，如果指针总是指向一个有效对象或者是null，你可以依靠null检查相当于有效性检查。

The rationale for the habit is that if a pointer always refers to either a valid object or is null, you can rely on null checks as equivalent to validity checks.

因为这个原因，Ada是一种常用于安全关键系统的语言，它初始化指向null的指针，并定义 delete 等效运算符自动设置其参数null。你的C ++正在模拟这种行为。

For this reason, Ada, a language often used in safety critical systems, initializes pointers to null and defines its delete equivalent operator to set its argument null automatically. Your C++ is simulating this behavior.

在实践中，这个学科的价值不是你想要的。一旦在很长一段时间，它防止了一个愚蠢的错误。一个很好的事情，但是，调试器显示的指针内容有意义。

In practice, the value of this discipline is not what you'd hope. Once in a long while it prevents a silly error. One nice thing, however, is that debugger displays of pointer content make sense.

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