找不到存储到地图中的值

Question

我基本上是一个字符一个字符地读取文件，当我遇到一个新的数字时，我会将它作为一个元素等于1的键存储在std::map中。遇到相同的数字的次数越多，我就会递增该键的元素：

if(intMap.count(singleCharacter)){
    //keyexist  just increment count else
    //cout<<"exist"<<endl;
                
    int newValue =  intMap.at(singleCharacter) + 1; //grabs the value that already exists and we need to incrmenet it by 1 and store the new value in the map.

    std::map<int, int>::iterator it = intMap.find(singleCharacter); //finds the single character and increments it by 1.

    if (it != intMap.end())
        it->second = newValue; //setting the new increment value into the element
}else{
    //doesnt exist and and we need to create it and incrmenet by 1
    //cout<<"doesnt exist"<<endl;
    intMap.insert(pair<int, int>(singleCharacter,1));
    cout<<singleCharacter <<" new made : "<<intMap.at(singleCharacter) <<endl;
    }
}

for (auto& p : intMap ) {
    cout << p.first<<": "<< p.second <<endl;; // "Karl", "George"
}

唯一的问题是，当我试图打印出映射中的所有值时，它会给我随机数字，而我不知道它们是从哪里来的。

这就是我正在读的文件：

An International Standard Book Number (ISBN) is a code of 10 characters, referred to as ISBN-10,                                                                             
 separated by dashes such as 0-7637-0798-8. An ISBN-10 consists of four parts: a group code, a publisher code,                                                                
 a code that uniquely identifies the book among those published by a particular publisher, and a check character.                                                             
 The check character is used to validate an ISBN. For the ISBN 0-7637-0798-8, the group code is 0,                                                                            
 which identifies the book as one from an English-speaking country. The publisher code 7637 is for "Jones and Bartlett Publishers

我得到的输出是：

48: 8                                                                                                                                                                          
49: 3                                                                                                                                                                          
51: 3                                                                                                                                                                          
54: 3                                                                                                                                                                          
55: 8                                                                                                                                                                          
56: 4                                                                                                                                                                          
57: 2  

我应该得到的输出应该是：

1: and the amount of times it was seen 

这对任何数字都是一样的。

Answer 1

您获得这些“随机”数字是因为您使用的是std::map<int,int>而不是std::map<char,int>。打印出来的是字符符号的ASCII数字代码和它们的计数。

因此，您需要更改映射的类型，或者将键转换回char

for (auto& p : intMap ) {
    cout << static_cast<char>(p.first) << ": "<< p.second <<endl;
}

注意：std::map::operator[]正是为这种情况设计的，在这种情况下，它会将未命中的值初始化为0，因此您的所有条件都可以替换为：

intMap[singleCharacter]++;

详细信息可以在this documentation中找到。