C++:初始化/候选构造函数的匹配构造函数不可行:需要单个参数,但没有提供参数

Question

我试图用C++实现一个链表,不知道如何修复下面给出的错误.我非常感谢任何有关调试的帮助,更重要的是,我对这个错误我不理解的任何基础概念的解释.谢谢.

这是我的错误:

linkedList.cpp:19:23: error: no matching constructor for initialization of 'NodeType'
        newnode = new NodeType;
                      ^
./linkedList.h:10:9: note: candidate constructor not viable: requires single argument 'str', but no arguments
      were provided
        NodeType(const std::string str);
        ^
./linkedList.h:4:7: note: candidate constructor (the implicit copy constructor) not viable: requires 1
      argument, but 0 were provided
class NodeType
      ^
linkedList.cpp:54:29: error: no matching constructor for initialization of 'NodeType'
    NodeType* newnode = new NodeType;
                            ^
./linkedList.h:10:9: note: candidate constructor not viable: requires single argument 'str', but no arguments
      were provided
        NodeType(const std::string str);
        ^
./linkedList.h:4:7: note: candidate constructor (the implicit copy constructor) not viable: requires 1
      argument, but 0 were provided
class NodeType
      ^

这是我的linkedList.h文件中的NodeType类:

  3 // define the node class
  4 class NodeType
  5 {
  6     private:
  7         std::string value;
  8         NodeType* next;
  9     public:
 10         NodeType(std::string str);
 11     friend class LinkedList;
 12 };

以下是linkedList.cpp文件中第一个错误的方法:

 10 LinkedList::LinkedList(const LinkedList& src)
 11 {
 12     head = NULL;
 13     NodeType* srccur; //node that is currently in src
 14     srccur = src.head;
 15 
 16     NodeType* pre = NULL; //predecessor of the new node
 17     while (srccur != NULL) // have not finished yet
 18     {   NodeType* newnode;
 19         newnode = new NodeType;
 20         if (newnode == NULL) //dynamic allocation failed
 21             { cout << "Memory allocation error" << endl;
 22                 exit(1);
 23             }
 24 
 25     newnode->value = srccur->value;
 26 
 27     if (pre == NULL)    //the new node becomes the 1st node
 28         head = newnode;
 29     else    // the new node is attached to the end
 30         pre->next = newnode;
 31 
 32     newnode->next = NULL;
 33 
 34     pre = newnode;
 35     srccur = srccur->next;
 36     }
 37 };

以下是linkList.cpp文件中第二个错误的方法:

 53 bool LinkedList::insertFirst(string v){
 54     NodeType* newnode = new NodeType;
 55 
 56     if (newnode == NULL) // dynamic allocation failed
 57     {
 58         return false;
 59     }
 60 
 61     newnode->value = v;
 62     newnode->next = head;
 63 
 64     head = newnode;
 65 
 66     return true;
 67 };

Answer 1

非常简单.查看你的构造函数NodeType(linkedList.h,第10行).它需要一个字符串.但是,当您创建NodeType(linkedList.cpp,第18行,第54行)的新实例时,您正在调用没有任何参数的构造函数.

这样做的正确方法是......

NodeType* newnode = new NodeType("Some string.");

如果您希望构造函数中的字符串参数是可选的,您可以通过将构造函数的头部原型更改为...来实现.

NodeType(std::string str="Some default value");

此外,您可以重载构造函数,其中一个不带参数,一个接受字符串,依此类推.

你知道,这是一个非常基本的原则.如果您是学生(正式或非正式),您将需要查看C++面向对象编程,特别是"构造函数".