未找到采用 c++ 类型的左手操作数的运算符

问：

需要帮助找出以下源代码的问题所在。我有一个类来计算多个字符，并将每个字符显示到控制台屏幕中。

但不幸的是，当我尝试编译时，我一直收到这个错误消息

错误 C2678：二进制“>>”：未找到采用类型为“std：：istream”的左操作数的运算符（或没有可接受的转换）

以下是源文件：

CharacterCounter.h

 #include <iostream>

 class CharacterCounter {
    public: 
      int fTotalNumberOfCharacters;
      int fCharacterCounts[256];  // hold all 256 byte values 

    public: 
      CharacterCounter();
      void count(unsigned char aCharacter);
      friend std::ostream& operator<<(std::ostream& aOStream, CharacterCounter& aCharacterCounter); 
    };

   }

字符计数器.cpp

    #include "CharacterCounter.h"
    #include <iostream>

    /// Constructor 
    CharacterCounter::CharacterCounter() {
      fTotalNumberOfCharacters = 0;
      for (int i=0; i < 256; i++) {
          fCharacterCounts[i] = i;
      } 
    }

    /// Counts the corresponding data member 
    void CharacterCounter::count(unsigned char aCharacter) {
      fTotalNumberOfCharacters++;
      fCharacterCounts[aCharacter]++;
    }

    /// Output stream displays characters greater than 0 
    std::ostream& operator<<(std::ostream& aOStream, const CharacterCounter& aCharacterCounter) {
      for (int i=0; i < 256; i++) {
        if (aCharacterCounter.fCharacterCounts[i] > 0) {
          int character = aCharacterCounter.fCharacterCounts[i]; 
          aOStream << (unsigned char)i << ":\t" << character << "\n"; 
        }
      } 

      return aOStream;
    }

主 .cpp

    #include <iostream>
    #include <string>
    #include "CharacterCounter.h"

    using namespace std; 

    int main() {

      CharacterCounter counter; 
      unsigned char character;

    while (cin >> counter) { **Compilation error focuses here**
       counter.count(character);
    }

    cout << counter; 
    system("pause");

    return 0;
   };