C++ read data from files

Question

Let's say I have a .txt file with this data in it:

1 Lipton 2  
2 CocaCola 2.5  
3 Pepsi 2

The ID for each item is before it and the price is after. After I read the file and it works, how should I do if I want to choose the ID 2 and display it's price multiplied by 2?

Possible duplicate of [Read file line by line](https://stackoverflow.com/questions/7868936/read-file-line-by-line) — Jamal Alkelani, May 07 '18 at 20:08
check the following link which is how to read files https://stackoverflow.com/questions/7868936/read-file-line-by-line — Jamal Alkelani, May 07 '18 at 20:09
You must *store* the information. Try it and get back to us if you have trouble. — Beta, May 07 '18 at 20:11
Read the file into a `std::map` that maps from the ID number to a struct that contains the name and price. — Barmar, May 07 '18 at 20:22
Search the internet for "c++ read file struct space separated". — Thomas Matthews, May 07 '18 at 20:22

score 1 · Accepted Answer · answered May 07 '18 at 20:28

One method is to store the data into a std::vector:

class Drink
{
    unsigned int id;
    std::string  name;
    double       price;
    friend std::istream& operator>>(std::istream& input, Drink& d);
};

std::istream& operator>>(std::istream& input, Drink& d)
{
    input >> d.id;
    input >> d.name;
    input >> d.price;
    return input;
}

Your input code would like like this:

std::ifstream drink_file("drinks.txt");
std::vector<Drink> database;
Drink d;
while (drink_file >> d)
{
    database.push_back(d);
}

You could search the database for a drink with ID==2:

size_t quantity = database.size();
for (size_t index = 0; index < quantity; ++index)
{
    if (database[index].id == 2)
    {
       // Do something with record ID 2.
       break;
    }
}

C++ read data from files

1 Answers1