c++ - 错误 C2593 : 'operator =' is ambiguous For string template

Question

我的部分模板不断收到此错误，因为它工作正常。我很想自己处理这个错误，但我什至不知道这意味着什么。也许我的运算符重载语法不正确？但即使没有我的运算符加载方法，我仍然会遇到同样的错误

node.h(12): error C2593: 'operator =' is ambiguous
  c:\program files (x86)\microsoft visual studio 11.0\vc\include\xstring(992): could be 'std::basic_string<_Elem,_Traits,_Alloc> &std::basic_string<_Elem,_Traits,_Alloc>::operator =(_Elem)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>,
1>              _Alloc=std::allocator<char>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 11.0\vc\include\xstring(987): or       'std::basic_string<_Elem,_Traits,_Alloc> &std::basic_string<_Elem,_Traits,_Alloc>::operator =(const _Elem *)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>,
1>              _Alloc=std::allocator<char>
1>          ]

c:\program files (x86)\microsoft visual studio 11.0\vc\include\xstring(987): or       'std::basic_string<_Elem,_Traits,_Alloc> &std::basic_string<_Elem,_Traits,_Alloc>::operator =(const _Elem *)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>,
1>              _Alloc=std::allocator<char>
1>          ]
1>          while trying to match the argument list '(std::string, int)'
1>          c:\users\aaron\documents\visual studio 2012\projects\redblacktreefinal\redblacktreefinal\node.h(10) : while compiling class template member function 'Node<T>::Node(void)'
1>          with
1>          [
1>              T=std::string
1>          ]
1>          c:\users\aaron\documents\visual studio 2012\projects\redblacktreefinal\redblacktreefinal\redblacktree.cpp(145) : see reference to function template instantiation 'Node<T>::Node(void)' being compiled
1>          with
1>          [
1>              T=std::string
1>          ]
1>          c:\users\aaron\documents\visual studio 2012\projects\redblacktreefinal\redblacktreefinal\redblacktree.cpp(203) : see reference to class template instantiation 'Node<T>' being compiled
1>          with
1>          [
1>              T=std::string
1>          ]
1>          c:\users\aaron\documents\visual studio 2012\projects\redblacktreefinal\redblacktreefinal\redblacktree.cpp(197) : while compiling class template member function 'bool RedBlackTree<T>::remove(T)'
1>          with
1>          [
1>              T=std::string
1>          ]
1>          c:\users\aaron\documents\visual studio 2012\projects\redblacktreefinal\redblacktreefinal\redblacktreefinal.cpp(240) : see reference to function template instantiation 'bool RedBlackTree<T>::remove(T)' being compiled
1>          with
1>          [
1>              T=std::string
1>          ]
1>          c:\users\aaron\documents\visual studio 2012\projects\redblacktreefinal\redblacktreefinal\redblacktreefinal.cpp(213) : see reference to class template instantiation 'RedBlackTree<T>' being compiled
1>          with
1>          [
1>              T=std::string
1>          ]

我的node.h文件

#include <cstdlib>
#include <cstring>

template <class T>
class Node {

    public :

        Node<T>(void) {
            parent  = NULL;
            left    = NULL;
            right   = NULL;
            data    = NULL;
            isBlack = false;
        }
        Node<T>(T x){
            parent  = NULL;
            left    = NULL;
            right   = NULL;
            data    = x;
            isBlack = false; 
        }
        Node<T>(const Node<T>* & nd){
            parent  = nd->parent;
            left    = nd->left;
            right   = nd->right;
            data    = nd->data;
            isBlack = nd->isBlack;
        }

        Node<T> & Node<T>::operator = (const Node<T>* & nd){
            parent  = nd->parent;
            left    = nd->left;
            right   = nd->right;
            data    = nd->data;
            isBlack = nd->isBlack;
            return* this;
        }

        Node<T>* parent;
        Node<T>* left;
        Node<T>* right;

        T   data;
        bool  isBlack;

    private :

};

如何使用

void part2()
{
  cout << endl << endl << "REDBLACKTREE<STRING>";
  cout << endl << "insert file and print contents (load, dump)" << endl;
  RedBlackTree<string> rb;
  string fname = "part2.txt"; //should contain strings
  int n = 0;

  // read file and load contents into tree
  string* arr = readFile<string>(fname, n);
  rb.load(arr, n);

  // read contents from tree into array
  int out_n = 0;
  string* out = rb.dump(out_n);

  // print dumped contents
  int count = 0;
  for(int i=0; i < out_n; i++){
         if(count % 5 == 0){
                 cout << endl;
         }
         cout << left << setw(13) << out[i];
         count ++;
  }
  cout << endl;
  statsPrint(rb, 174, 5, 9, true);

  // remove all items from tree
  cout << endl << endl << "empty tree one item at a time";
  for(int i=0; i < n; i++){
         rb.remove(arr[i]);
  }
  statsPrint(rb, 0, 0, 0, true);

  delete[] arr;
  delete[] out;
}

Answer 1

问题是:

    Node<T>(void) {
        parent  = NULL;
        left    = NULL;
        right   = NULL;
        data    = NULL; // <----- Remove this line - this is causing the errors
        isBlack = false;
    }

编辑:这是一个隔离此错误的小 C++ 程序:

#include <string>

int main()
{
  std::string data;
  data = NULL; // error: ambiguous overload for ‘operator=’ in ‘data = 0’
  return 0;
}

根据错误消息，NULL(即 0)似乎可以解释为 char 或 常量 *字符。因此出现“错误:‘operator=’消息的不明确重载。

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~

原帖:

这是 operator= 重载的奇怪签名:

Node<T> & Node<T>::operator = (const Node<T>* & nd)

通常只是

Node<T> & Node<T>::operator = (const Node<T> & nd)

没有星号。这可能会消除编译器提示的歧义。当然，您必须在该函数中将 -> 更改为 .。