Reading from a file is not returning the correct number of objects

I am coding a Discord bot, using the D++ library, that tracks the amount of health an entity has, and allows users on the server to modify the health of said entities.

My problem is with my command that handles when a user wants to modify the health value. The contents of the .txt file are as follows:

Zombie:120
Skeleton:200
Vampire:500

If the user enters the command to modify the Vampire's health by -100, the file will instead look like this instead of lowering the vampire's health from 500 to 400:

Zombie:120
200
Vampire:500

Here is the relevant code:

if (event.command.get_command_name() == "change")
{
    int count = 0;
    vector<string> entities;
    vector<int> health;
    string myText;
    string nameChoice = get<string>(event.get_parameter("user"));
    ifstream MyReadFile("entities.txt");
    while(getline(MyReadFile, myText, ':'))
    {
        if (count == 0)
        {
            entities.push_back(myText);
            count += 1;
        }
        else if (count == 1)
        {
            if (entities.back() == nameChoice)
            {
                int temp = stoi(myText);
                temp += get<int64_t>(event.get_parameter("numeral"));
                cout << "temp" << temp;
                health.push_back(temp);
                count = 0;
            }
            else
            {
                health.push_back(stoi(myText));
                count = 0;
            }
        }
    }
    MyReadFile.close();
    ofstream MyFile("entities.txt", ios_base::out);
    for (int i = 0; i < entities.size(); i++)
    {
        MyFile << entities[i] << ":";
        MyFile << health[i] << "\n";
    }
    
    MyFile.close();
}

Through some debugging, I have found out that the while loop is only looping 4 times, when it seemingly should be doing so 6 times.

As I am still a beginner at C++, I have been struggling to understand why, so I'd appreciate any guidance you could offer.

> c++
> while(getline(MyReadFile, myText, ':'))
>

What's happening here is a demonstration of the Golden Rule Of Computer Programming, which says:

"Your computer always does exactly what you tell it to do instead of what you want it to do."

Here, you told your computer: "read from myReadFile until the next : character". So this is what your computer does here.

If the contents of the file are:

zombie:100
skeleton:200
mummy:300

Then:

• The first time in this while loop, your computer reads "zombie" and puts that into your myText (everything up until the first :).

• The second time in this while loop, it reads "100\nskeleton" and puts that into your myText (everything up until the second :).

• The third time in this while loop, it reads "200\nmummy" and puts that into your myText (everything up until the third :).

• The fourth time in this while loop, it reads "300" and puts that into your myText (everything up until the end-of-file).

This is what you told your computer to do: read until the next : character, every time, so that's what your computer does.

It's pretty clear that this is not what you wanted your computer to do, but that's what you told it to do, so that's what it does.

> I have been struggling to understand why

That's why, for the reasons explained above. std::getline() reads input until a specific character gets read. End of story. No exceptions. By default it's the \n character, but an optional third parameter specifies a different character. If it is specified it completely replaces the default \n character, it does not supplement it.

Any time you feel the need to use parallel arrays to hold related values, you should instead use a single array that holds a struct/class type.

That said, you are not using std::getline() correctly. You are telling it to read only until the next : character, without any regards to line breaks. You are expecting it to stop reading when it encounters either ':' or '\n', but that is simply not how it works.

When dealing with line-oriented data, you should read a whole line first, and then parse the line as needed.

Try something more like this:

if (event.command.get_command_name() == "change")
{
    struct entity
    {
        string name;
        int health;
    };

    vector<entity> entities;
    string line, nameChoice = get<string>(event.get_parameter("user"));

    ifstream MyReadFile("entities.txt");
    while (getline(MyReadFile, line))
    {
        istringstream iss(line);

        entity e;
        getline(iss, e.name, ':');
        iss >> e.health;

        if (e.name == nameChoice)
        {
            e.health += get<int64_t>(event.get_parameter("numeral"));
            cout << "temp" << e.health;
        }

        entities.push_back(e);
    }
    MyReadFile.close();

    ofstream MyFile("entities.txt");
    for (size_t i = 0; i < entities.size(); ++i)
    {
        MyFile << entities[i].name << ':' << entities[i].health << '\n';
    }
    
    MyFile.close();
}

Alternatively, you can omit the std::istringstream if you instead simply ignore() the next line break after reading each health value, eg:

if (event.command.get_command_name() == "change")
{
    struct entity
    {
        string name;
        int health;
    };

    vector<entity> entities;
    string nameChoice = get<string>(event.get_parameter("user"));
    entity e;

    ifstream MyReadFile("entities.txt");
    while (getline(MyReadFile, e.name, ':'))
    {
        MyReadFile >> e.health;
        MyReadFile.ignore(numeric_limits<streamsize>::max(), '\n');

        if (e.name == nameChoice)
        {
            e.health += get<int64_t>(event.get_parameter("numeral"));
            cout << "temp" << e.health;
        }

        entities.push_back(e);
    }
    MyReadFile.close();

    ofstream MyFile("entities.txt");
    for (size_t i = 0; i < entities.size(); ++i)
    {
        MyFile << entities[i].name << ':' << entities[i].health << '\n';
    }
    
    MyFile.close();
}

Alternatively, you can get rid of the std::vector altogether if you write to a separate file while reading the original file, eg:

if (event.command.get_command_name() == "change")
{
    string nameChoice = get<string>(event.get_parameter("user"));
    string entity;
    int health;

    ifstream MyReadFile("entities.txt");
    ofstream MyFile("new_entities.txt");

    while (getline(MyReadFile, entity, ':'))
    {
        MyReadFile >> health;
        MyReadFile.ignore(numeric_limits<streamsize>::max(), '\n');

        if (entity == nameChoice)
        {
            health += get<int64_t>(event.get_parameter("numeral"));
            cout << "temp" << health;
        }

        MyFile << entity << ':' << health << '\n';
    }

    MyReadFile.close();    
    MyFile.close();

    remove("entities.txt");
    rename("new_entities.txt", "entities.txt");	
}