Extra chararcters when writing to a file from a struct

Question

I have a class Unit. An object of this class has name, id, budget and other stuff. I want to save the name and the budget in a .txt file at position (i-1). I created struct called Unit2:

struct Unit2{

    string name;
    int budget;
};

My file.write function:

void writeBudgets(Unit name,int i) {
    ofstream file("C:\\Users\\User\\Desktop\\budgets.txt");
    Unit2 p;
    p.name  = name.getName();        //get name from the class Unit
    p.budget = name.getBudget();     //same for budget
    file.seekp((i-1)*sizeof(Unit2));
    file.write(reinterpret_cast<char*> (&p),sizeof(Unit2));
    file.close();
}

In the main I create object of Unit "a" with name "asd" and budget 120. When I use writeBudgets function an extra characters are added to my file. For example writeBudgets(a,2); gives me this hÆPasd ÌÌÌÌÌÌÌÌÌÌÌÌ Œ .What should I do?

Answer 1

You can't write a std::string like that to a file, as the std::string object doesn't have the actual string inside itself, but a pointer to the string together with its length.

What you should do is learn more about the C++ input/output library, then you can make a custom output operator << for your structure.

---

You make a custom operator<< function:

std::ostream& operator<<(std::ostream& os, const Unit2& unit)
{
    // Write the number
    os << unit.budget;

    // And finally write the actual string
    os << unit.name << '\n';

    return os;
}

With the above function, you can now do eg

Unit2 myUnit = { "Some Name", 123 };
std::cout << myUnit;

and it will print on the standard output

123 Some Name

To read the structure, you make a corresponding input operator function:

std::istream& operator>>(std::istream& is, Unit2& unit)
{
    // Read the number
    is >> unit.budget;

    // The remainder of the line is the name, use std::getline to read it
    std::getline(is, unit.name);

    return is;
}