[英]What is wrong with my ctor using linked list and templates?
I am trying to practice a little bit with cpp and want to make a class of linked list and than to manipulate it reverse it, finding circle and etc. but I can't understand what is the problem with my ctor/ 我正在尝试与cpp一起练习一点,并想制作一类链表,而不是对其进行反向操作,查找圆形等。但是我不明白我的ctor /是什么问题
I have this main: 我有这个主要的:
#include "list.h"
#include <iostream>
using namespace std;
int main () {
int x = 10;
ListNode<int> node4();
ListNode<int> node3(10 ,node4);
}
while this is "list.h" : 这是“ list.h”时:
#ifndef LIST_NODE_H
#define LIST_NODE_H
#include <iostream>
using namespace std;
template <class T>
class ListNode {
ListNode* next;
T data;
public:
ListNode<T>( T dat = 0 ,const ListNode<T> &nex = NULL):data(dat),next(nex){};
};
#endif
I can't understand why this line: ListNode<int> node3(10 ,node4);
我不明白为什么这行: ListNode<int> node3(10 ,node4);
makes this errors, what is the problem? 出现此错误,是什么问题?
list.cpp: In function 'int main()': list.cpp:12:33: error: invalid conversion from 'ListNode ( )()' to 'int' [-fpermissive] list.h:15:3: error: initializing argument 1 of 'ListNode::ListNode(T, const ListNode&) [with T = int]' [-fpermissive] list.cpp:12:33: warning: passing NULL to non-pointer argument 1 of 'ListNode::ListNode(T, const ListNode&) [with T = int]' [-Wconversion-null] list.cpp:12:33: error: recursive evaluation of default argument for 'ListNode::ListNode(T, const ListNode&) [with T = int]' list.h:15:3: warning: in passing argument 2 of 'ListNode::ListNode(T, const ListNode&) [with T = int]' [enabled by default] list.h: In constructor 'ListNode::ListNode(T, const ListNode&) [with T = int]': list.cpp:12:33: instantiated from here list.h:15:76: error: cannot convert 'const ListNode' to 'ListNode ' in initialization list.cpp:在函数'int main()'中:list.cpp:12:33:错误:从'ListNode( )()'到'int'[-fpermissive] list.h:15:3:错误的转换无效:初始化'ListNode :: ListNode(T,const ListNode&)[[T = int]“的参数1 [-fpermissive] list.cpp:12:33:警告:将NULL传递给'ListNode ::的非指针参数1 ListNode(T,const ListNode&)[with T = int]'[-Wconversion-null] list.cpp:12:33:错误:递归评估'ListNode :: ListNode(T,const ListNode&)[]的默认参数= int]'list.h:15:3:警告:传递'ListNode :: ListNode(T,const ListNode&)的参数2 [T = int]'[默认启用] list.h:在构造函数'ListNode中:: ListNode(T,const ListNode&)[with T = int]':list.cpp:12:33:从此处实例化list.h:15:76:错误:初始化时无法将'const ListNode'转换为'ListNode '
You have a number of errors with your code: 您的代码有很多错误:
In your constructor you have a null
reference as your default value, which is invalid (see here ). 在构造函数中,您有一个null
引用作为默认值,这是无效的(请参阅此处 )。
For a constructor with no arguments you need to omit the ()
(you can read about why here ) 对于不带参数的构造函数,您需要省略()
(您可以在此处了解原因)
Something like this should work: 这样的事情应该起作用:
using namespace std;
template <class T>
class ListNode {
ListNode* next;
T data;
public:
ListNode<T>( T dat = 0 ,ListNode<T> * nex = NULL):data(dat),next(nex){};
};
int main(){
ListNode<int> node4;
ListNode<int> node3(10, &node4);
}
There are a couple of problems here. 这里有两个问题。
First you don't need ListNode<T>()
simpley ListNode(...)
for the constructor. 首先,构造函数不需要ListNode<T>()
简单的ListNode(...)
。
Second you can't have a defalut for a reference parameter to null if there is the potential for nex to be null it needs to be a pointer. 其次,如果nex可能为null,则您不能将引用参数默认为null,而必须将其作为指针。
Default parameters are evil (IMO). 默认参数是邪恶的(IMO)。
(just a thought) Create different constructors (one with no parameters, one with parameters, ... ) (只是一个想法)创建不同的构造函数(一个不带参数的构造器,一个不带参数的构造器,...)
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