带有指针值的C++映射

C++ map with pointer value

本文关键字：C++ 映射 指针      更新时间：2023-10-16

我尝试读取一个字典文件，其中每一行都包含单词id、单词和频率，用空格分隔。问题是，用来存储单词的地图具有相同的值。如果你能帮我，我非常感激。

typedef struct{
    int id;
    int count;
    char* word;
} WORD;
//read file
std::map<int, WORD*> readWordMap(char* file_name)
{
    std::ifstream infile(file_name, std::ifstream::in);
    std::cout<<"word map read file:"<<file_name<<std::endl;
    if (! infile) {
        std::cerr<<"oops! unable to open file "<<file_name<<std::endl;
        exit(-1);
     }
     std::map<int, WORD*> map;
     std::vector<std::string> tokens;
     std::string line;
     char word[100];
     int size;
     while (std::getline(infile, line)) {
         size =  (int)split(line, tokens, ' ');
         WORD* entry = (WORD*) malloc(sizeof(WORD*));
         entry->id = atoi(tokens[0].c_str());
         entry->count = atoi(tokens[2].c_str());
         strcpy(word, tokens[1].c_str());
         entry->word = word;
         map[entry->id] = entry;
         std::cout<< entry->id<<" "<<entry->word<<" "<<entry->count<<std::endl;
      }
      infile.close();
      std::cout<<map.size()<<std::endl;
      std::map<int, WORD*>::const_iterator it;
      for (it = map.begin(); it != map.end(); it++) {
           std::cout<<(it->first)<<" "<<(it->second->word)<<std::endl;
      }
      return map;
}
//split string by a delimiter
size_t split(const std::string &txt, std::vector<std::string> &strs, char ch)
{
    size_t pos = txt.find( ch );
    size_t initialPos = 0;
    strs.clear();
    while( pos != std::string::npos ) {
        strs.push_back( txt.substr( initialPos, pos - initialPos + 1 ) );
        initialPos = pos + 1;
        pos = txt.find( ch, initialPos );
    } 
   strs.push_back( txt.substr( initialPos, std::min( pos, txt.size() ) - initialPos + 1      ) );
   return strs.size();
}

数据文件：

2 I  1
3 gave  1
4 him  1
5 the  3
6 book  3
7 .  3
8 He  2
9 read  1
10 loved  1

结果：

2 I  1
3 gave  1
4 him  1
5 the  3
6 book  3
7 .  3
8 He  2
9 read  1
10 loved  1
map size:9
2 loved 
3 loved 
4 loved 
5 loved 
6 loved 
7 loved 
8 loved 
9 loved 
10 loved 

WORD* entry = (WORD*) malloc(sizeof(WORD*));

分配一个CCD_ 1而不是整个CCD_。

编译器不断地分配条目，如果没有初始化为任何东西(它们都指向某个随机地址，该地址甚至可能不属于您的程序。(，然后您重复地将该指针添加到映射中。因此，地图上的所有第一个都指向同一位置(巧合地(。应该是

WORD* entry = new WORD;

这是一种更清洁的方式

struct WORD{
    int id;
    int count;
    std::string word;
};

while (std::getline(infile, line)) {
     WORD* entry = new WORD;
     std::istringstream iss(line);
     iss >> entry->id >> entry->word >> entry->count;
     map[entry->id] = entry;
     std::cout<< entry->id<<" "<<entry->word<<" "<<entry->count<<std::endl;
  }

您忘记在strcpy之前为WORD::word分配内存。您将char word[100]的地址分配给映射的所有项，这对所有项都是相同的。

 

最好使用std::string而不是C样式的字符串。此外，您可以使用std::stoi将字符串转换为整数。试试这个：

struct WORD{
    int id;
    int count;
    std::string word;
};
std::map<int, WORD> readWordMap(const std::string &file_name)
{
     ...
     std::map<int, WORD> map;
     ...
     while (std::getline(infile, line)) {
         ...
         WORD entry;
         entry.id = std::stoi(tokens[0]);
         entry.count = std::stoi(tokens[2]);
         entry.word = tokens[1];
         map[entry.id] = entry;
         ...
      }
      infile.close();
      ...
}
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