CODEWITHSUNDEEP
c++pointersdictionary
allen.lao
allen.lao

Reputation: 49

C++ map with pointer value

I try to read a dictionary file, in which each line contains word-id, word and frequency separated by a whitespace. The problem is that the map used to store words turned out have same value. I very appreciate if you can help me.

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();
}

Data file:

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

result:

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

Upvotes: 0

Views: 4371

Answers (2)

stardust
stardust

Reputation: 5988

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

allocates a WORD pointer not a whole WORD struct.

The compiler keeps allocating entry put it is not initalized to anything (they are all pointing to some random address which doesnt even belong to your program possibly. ) and you add that pointer to the map repeatedly. So all firsts of your map are pointing to the same location (coincidentaly). It should be

WORD* entry = new WORD;

This is a cleaner way of doing it

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;
  }

Upvotes: 1

masoud
masoud

Reputation: 56479

You forget to allocate memory for WORD::word before strcpy. And you are assigning the address of char word[100] to all items of the map which is same for all of them.

 

And it's better to use std::string instead of C-style strings. In addition you can use std::stoi to convert strings to integers. Try this:

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();
      ...
}

Upvotes: 1

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