错误：在 C++ 中从“Counter”转换为非标量类型“CountDn”

Posted 2023-02-23

【中文标题】错误：在 C++ 中从“Counter”转换为非标量类型“CountDn”

【英文标题】：error: conversion from 'Counter' to non-scalar type 'CountDn' in c++

【发布时间】：2017-08-16 02:40:47

【问题描述】：

#include <iostream>
using namespace std; 
class Counter

protected:
unsigned int count;
public:
    Counter ():count ()
   
    Counter (int c):count (c)
   
  unsigned int get_count () const
   return count;
  Counter operator ++ ()
  return Counter (++count);
  ;

  class CountDn:public Counter
  
  public:CountDn ():Counter () 
  CountDn (int c):Counter (c) 
  CountDn operator -- ()
  return CountDn (--count);
  ;

  int main ()
  
    CountDn c1;
    CountDn c2 (100);
    cout << "\nc1=" << c1.get_count ();
    cout << "\nc2=" << c2.get_count ();
    ++c1;
    ++c1;
    ++c1;
    cout << "\nc1=" << c1.get_count ();
    --c2;
    --c2;
    cout << "\n c2=" << c2.get_count ();
    CountDn c3 = ++c2;
    cout << "\n c3=" << c3.get_count ();
    cout << endl;
    return 0;

当我使用重载的“++”运算符时出现错误，而当我使用“--”时效果很好。

错误信息是

37:14: error: conversion from ‘Counter’ to non-scalar type ‘CountDn’ requested
 CountDn c3 = ++c2;

为什么会出现此错误？ 这个错误是什么意思，我该如何解决？

【参考方案1】：

当我使用重载的 '++' 运算符时出现错误，而当我使用 '--' 时效果很好。

您在 CountDn 类中实现了运算符重载 -- 但没有 ++

CountDn 类中缺少 ++ 的运算符重载 你必须添加

CountDn operator ++ ()
return CountDn (++count);

修改后

#include <iostream>
using namespace std;
class Counter

protected:
    unsigned int count;
public:
    Counter ():count ()
     
    Counter (int c):count (c)
     
    unsigned int get_count () const
     return count;
    Counter operator ++ ()
    return Counter (++count);

;

class CountDn:public Counter

public:CountDn ():Counter () 
    CountDn (int c):Counter (c) 
    CountDn operator -- ()
    return CountDn (--count);
    CountDn operator ++ ()
    return CountDn (++count);
;

int main ()

    CountDn c1;
    CountDn c2 (100);
    cout << "\nc1=" << c1.get_count ();
    cout << "\nc2=" << c2.get_count ();
    ++c1;
    ++c1;
    ++c1;
    cout << "\nc1=" << c1.get_count ();
    --c2;
    --c2;
    cout << "\n c2=" << c2.get_count ();
    CountDn c3 = ++c2;
    cout << "\n c3=" << c3.get_count ();
    cout << endl;
    return 0;

输出

c1=0
c2=100
c1=3
 c2=98
 c3=99
Program ended with exit code: 0

【参考方案2】：

结果

Counter operator ++ ()
    return Counter (++count);

属于Counter 类型，并且没有从Counter 到CountDn 的转换。 以下行编译正常：

Counter c3 = ++c2;