我认为followig片段中的printList函数接收指针作为参数。因此，它将修改head指针。但实际上，事实并非如此。否则，第二个printList函数根本无法打印节点，因为head指针已在第一个NULL函数中移至printList。
ListNode * head = new ListNode(-1);
push(head, 5);
push(head, 20);
push(head, 4);
push(head, 3);
push(head, 30);
printf("%x", head);
printList(head);
printf("%x", head);
void printList(ListNode *head) {
while (head != NULL) {
printf("%d ", head->val);
head = head->next;
}
printf("\n");
}
答案 0 :(得分：5)
C ++具有值语义传递。public function mostvotedans()
{
$this->db->select('open_id_fk, COUNT(*) as total');
$this->db->group_by('open_id_fk');
$this->db->order_by('total', 'desc');
$query = $this->db->get('voting_ip', 5);
return $query;
$query = $this->db->query("SELECT * FROM country WHERE open_id_fk=open_id;");
return $query;
}
对调用方没有影响，因为head = head->next;是head函数的本地。从这个意义上讲，传递指针与传递printList或int没有什么不同。您将获得传递的对象的本地副本。区别在于指针允许您引用非本地对象。
答案 1 :(得分：4)
参数<!doctype html>
<html>
<head>
<title>Darren's BBC</title>
<meta charset="utf-8" />
<meta http-equiv="Content-type" content="text/html; charset=utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1" />
<style type="text/css">
body {
margin:0;
background-color:violet;
/* This ensures the topbar stretches all the way across the screen and fills the top */
}
#topbar {
background-color:rgb(255,255,255);
width:100%;
height:40px;
color:black;
font-family:arial,helvetica,sans-serif;
font-weight:bold;
font-size:0.8em;
}
.fixedwidth {
width:1000px;
margin:0 auto;
}
#logodiv {
padding-top:4px;
padding-right:5px;
padding-bottom:4px;
float:left;
border-right:1px solid #DDDDDD;
}
#signindiv {
padding:8px 85px 11px 15px;
float:left;
border-right:1px solid #DDDDDD;
}
#signindiv img {
position:relative;
top:3px;
padding-right:2px;
}
#menudiv ul {
margin:0;
}
#menudiv li {
padding:14px 17px 10px 17px;
list-style:none;
float:left;
border-right:1px solid #DDDDDD;
}
#searchdiv {
float:left;
padding:8px 0 0 10px;
}
#searchdiv input {
border:none;
background-color:#E4E4E4;
height:24px;
width:190px;
font-weight:bold;
font-size:0.9em;
padding:0 5px 0 5px;
background-image:url("images/search.png");
background-repeat:no-repeat;
background-position:right center;
}
#newsbar {
background-color:#BB1919;
height:55px;
}
#newsbar p {
margin:0;
font-size:2.7em;
color:white;
font-family:Verdana, Geneva, sans-serif;
padding-left:50px;
}
.break {
clear:both;
}
#topicdiv {
margin:0;
background-color:#A91717;
width:100%;
height:37px;
}
#topicdiv ul {
margin:0;
padding:12px 0 5px 37px;
}
#topicdiv li {
color:white;
font-family:Arial, Helvetica, sans-serif;
font-size:1em;
list-style:none;
float:left;
border-right:1px solid #B73C3C;
padding-left:11px;
padding-right:11px;
}
</style>
</head>
<body>
<div id="container">
<div id="topbar">
<div class="fixedwidth">
<div id="logodiv">
<img src="images/bbclogo.png" />
</div>
<div id="signindiv">
<img src="images/signin.png" /> Sign In
</div>
<div id="menudiv">
<ul>
<li>News</li>
<li>Sport</li>
<li>Weather</li>
<li>Shop</li>
<li>Earth</li>
<li>Travel</li>
<li>More...</li>
</ul>
</div>
<div id="searchdiv">
<input type="text" placeholder="Search" />
</div>
<div class="break"></div>
<div id="newsbar">
<p>NEWS</p>
</div>
<div class="break"></div>
<div id="topicdiv">
<ul>
<li>Home</li>
<li>Video</li>
<li>World</li>
<li>Asia</li>
<li>UK</li>
<li>Business</li>
<li>Tech</li>
<li>Science</li>
<li>Magazine</li>
<li>Entertainment & Arts</li>
<li>Health</li>
<li>World News TV</li>
<li style="border-right:none">More...</li>
</ul>
</div>
</div>
</div>
</div>
</body>
</html>
获取指针的副本。 ListNode* head然后只修改该副本，而不是传递给函数的原始指针。
如果您需要修改原始指针，请将引用传递给它：head =
答案 2 :(得分：3)
通过这个，您可以从指针获得副本 如果你想修改指针本身你可以写这样的东西。
list2获取指针的目的是避免复制对象本身，并且当值可以为nullptr时，通过指针而不是引用来获取它。