I am working on a project to store class objects in a dynamically allocated array. Now instead of users setting objects' values, I am trying to read object's values from a text file. There are 10 objects stored in the file and I want to read 8 objects and then insert them in my dynamic array. This is my class:

class Person {
private:
    std::string name;
    double age;

public:
    // Constructor
    Stock(const std::string& name = "", double age = 0)
    {
        this->name = name;
        this->age = age;
    }

    // copy constructor
    Stock(const Stock& s)
    {
        this->name = s.name;
        this->age = s.age;
    }

    // Display function
    void display() const
    {
        std::cout << "Name is " << name << ", "
        << "Age is " << age << ".\n";
    }

    // get functions
    std::string getName() const
    {
        return name;
    }
    double getAge() const
    {
        return age;
    }

And my text file looks like this:

Tony
25
Cap 
30
Loki & Sylvi
20
...

How can I read these lines into 8 separate objects?

CodePudding user response：

It appears you have not actually compiled the code provided, since there are problems with it.

There are different ways to serialize/deserialize data. Here is one way, which may be sufficient for your needs.

This code allows constructing a Person from an istream&. Another way to provide a static class factory function to construct a Person from an istream&, which is probably more common.

Once constructed, the Person can be added to a vector, which is the dynamic array in C .

#include <iostream>
#include <sstream>
#include <stdexcept>
#include <string>
#include <utility>
#include <vector>

using std::cout;
using std::getline;
using std::istream;
using std::istringstream;
using std::move;
using std::ostream;
using std::runtime_error;
using std::string;
using std::vector;

namespace {

char const* data =
R"(Tony
25
Cap 
30
Loki & Sylvi
20
Bob 1
20
Bob 2
30
Bob 3
40
Bob 4
50
Bob 5
60
Bob 6
70
Bob 7
80
)";

auto get_string(istream& in) -> string {
    string result;
    if (getline(in, result)) return result;
    throw runtime_error("get_string");
}

auto get_double(istream& in) -> double {
    string line;
    if (!getline(in, line))
        throw runtime_error("get_double");

    istringstream ss(line);
    double result;
    if (!(ss >> result))
        throw runtime_error("get_double");

    return result;
}

class Person final {
    string _name;
    double _age;

public:
    Person(string name_ = "", double age_ = 0) : _name{move(name_)}, _age{age_} { }
    Person(Person const& s) : _name{s._name}, _age{s._age} { }
    Person(istream& in) : _name{get_string(in)}, _age{get_double(in)} { }

    void print(ostream& out) const {
        out << "Name is " << _name << ", " << "Age is " << _age << ".";
    }

    auto name() const -> string { return _name; }
    auto age() const -> double { return _age; }
};

auto operator<<(ostream& out, Person const& p) -> ostream& {
    p.print(out);
    return out;
}

auto operator<<(ostream& out, vector<Person> const& v) -> ostream& {
    for (auto&& p : v) {
        out << p << "\n";
    }
    return out;
}

} // anon

int main() {
    istringstream ss(data);
    auto tony = Person(ss);
    auto cap = Person(ss);
    auto loki_sylvi = Person(ss);
    cout << tony << "\n";
    cout << cap << "\n";
    cout << loki_sylvi << "\n";

    vector<Person> peeps;
    peeps.emplace_back(ss);
    peeps.emplace_back(ss);
    peeps.emplace_back(ss);
    cout << peeps << "\n";
}

CodePudding user response：

If I'd need to save an object to a file, I'd write the raw object to the file:

std::ofstream file("ofile.txt", std::ios::binary, std::ios::trunc);
file.write(&myPerson, (&myPerson)[1]);

And then read the file and cast it to a Person class