c++ - 如何将 char 设置为函数？我对语法感到困惑... set max_freq(map frequency)

Question

你好，当我设置 <char> (Function(map<char ,int>...) 时，我不知道 set 是如何工作的编辑:

//Set map
map<char, int> frequency;

其次:

map<char, int> count_chars(const string input) {
  // Given a map
  map<char, int> frequency;    
  // Populate it with the count of each character in the input
  //for loop to populate plus count
  for(int i = 0; i < size; i++){
      frequency[input[i]]++;
  }

  return frequency;
}

第三:

//Find highest occurence of character
char max_freq(map<char, int> frequency) {
  int key = 0;
  for (pair<char, int> elements : frequency){
     // highest = element.first;
      if(key <= elements.second){
          key = elements.second;
          highest = elements.first;
      }
  }
  return highest;
}

最后:

//I added set<char> s into the code below and it solved the syntax error. Any better solutions?
enter code here
// Below is what I wrote, I am supposed to find max occurrences of the character but I think I do not understand the syntax.
set<char> max_freq(map<char, int> frequency)
{
    char high;
    int key = 0;
    for (pair<char, int> elements : frequency)
    {
        if (key <= elements.second)
        {
            key = elements.second;
            high = elements.first;
            frequency[high];
        }
    }
    return frequency;
}

我一直收到这个错误:

Map.cpp:117:12: error: could not convert 'frequency' from 'std::map' to 'std::set' return frequency;

Answer 1

这是你的函数签名:

set<char> max_freq(map<char, int> frequency)

这个签名说的是:

"max_freq 是一个函数，它按值获取类型为 map<char, int> 的对象，并返回类型为 set<char> 的对象。"。

这意味着你返回的对象类型必须是set<char>或者它必须可以隐式转换为该类型。但是您返回的是 map<char, int> 类型的对象, 这是无效的。要么更改签名以满足您的需要，要么制作一个兼容类型的对象并将其返回。