c++ - 函数中不匹配 'operator=='

Question

我正在做一个 caesar decipher 项目，在 CaesarDecipher 函数中，我在编译时不断收到这个错误:

error: no match for ‘operator==’ in ‘textInit.std::basic_string<_CharT, _Traits, >_Alloc>::operator[] [with _CharT = char, _Traits = std::char_traits, _Alloc >= std::allocator](((long unsigned int)i)) == alphabet[j]’

这是该函数的代码:

string CipherMessage::CaesarDecipher(string key)
{
  int keyValue;
  int charValue;
  string textInit = m_text;
  string textFinal;
  // Initializes an array containing the alphabet. A=index 0, B=index 1, etc
  string alphabet[26] = {"A","B","C","D","E","F","G","H","I","J","K","L","M","N","\
O","P","Q","R","S","T","U","V","W","X","Y","Z"};

  for (int i=0; i<=25; i++){
    if (alphabet[i] == key)
      keyValue = i;
  }
for (int i=0; i<=textInit.length(); i++){
    for (int j=0; j<=25; j++){
      if (textInit[i] == alphabet[j])   // Error occurs here
        charValue = j;
    }
    charValue = (charValue+keyValue)%26;
    for (int j=0; j<=25; j++){
      if (charValue == j)
        textFinal += alphabet[j];
    }
  }
  cout << "Final " << textFinal << endl;

  return textFinal;
}

有人能帮忙吗？

Answer 1

你可能打算像这样声明alphabet

string alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

删除此错误消息。

正如在评论中提到的，您改为声明了一个包含 26 个完整 string 的数组，但是从 textInit[i] 进行索引实际上会返回一个 char 类型(不能反过来合理地与 std::string 进行比较)。