Iterate over array of objects from txt file - c++

Question

I have file with records separated by comas:
cities.txt:
1,NYC
2,ABQ
...
I would like to iterate over each row: ids and names. I have created the code:
#include <iostream>
#include <string>
using namespace std;
class City {
int id;
string name;
public:
City() {}
City(int id, int name)
{
this->id = id;
this->name = name;
}
void load_file()
{
ifstream v_file("cities.txt");
if (v_file.is_open()) {
while (!v_file.eof()) {
//...
}
}
v_file.close();
}
}
int main()
{
City array_city[1000];
array_city.load_file();
return 0;
}
Could you tell me how to load all rows to array array_city and iterate over it? I don't know what to place in while block in load_file method. I don't know weather, the method load_file should have void type. Unfortunately I have to do it on arrays.

Answer 1

It's not a good idea to use EOF in a while loop. Read more in Why is iostream::eof inside a loop condition considered wrong?
In c++, vectors should be preferred over arrays. However, your teacher knows something more to suggest using an array here. For that reason I am providing a solution with an array:
Read the file line by line
Extract the id and the string
Assign it to the i-th cell of the array
Code:
#include <iostream>
#include <string>
#include <fstream>
using namespace std;
class City {
int id;
string name;
public:
City() {}
City(int id, string name) : id(id), name(name)
{
}
void print()
{
cout << "ID = " << id << ", name = " << name << endl;
}
};
void load_file(City* cities, const int n)
{
ifstream v_file("cities.txt");
if (v_file.is_open()) {
int number, i = 0;
string str;
char c;
while (v_file >> number >> c >> str && c == ',' && i < n)
{
//cout << number << " " << str << endl;
cities[i++] = {number, str};
}
}
v_file.close();
}
int main()
{
City cities[4]; // assuming there are 4 cities in the file
load_file(cities, 4);
for(unsigned int i = 0; i < 4; ++i)
cities[i].print();
return 0;
}
Same solution with std::vector, if you are interested. =) If you haven't been taught about them, I suggest you skip that part and come back later when you do that in the course.
Use a vector of City. Read the file line by line, and push back into the vector every line you read, by constructing an instance of your class, and you are done!
Example:
#include <iostream>
#include <string>
#include <fstream>
#include <vector>
using namespace std;
class City {
int id;
string name;
public:
City() {}
City(int id, string name) : id(id), name(name)
{
}
void print()
{
cout << "ID = " << id << ", name = " << name << endl;
}
};
void load_file(vector<City>& cities)
{
ifstream v_file("cities.txt");
if (v_file.is_open()) {
int number;
string str;
char c;
while (v_file >> number >> c >> str && c == ',' && i < n)
{
//cout << number << " " << str << endl;
cities.push_back({number, str});
}
}
v_file.close();
}
int main()
{
vector<City> cities;
load_file(cities);
for(unsigned int i = 0; i < cities.size(); ++i)
cities[i].print();
return 0;
}
Input:
Georgioss-MacBook-Pro:~ gsamaras$ cat cities.txt
1,NYC
2,ABQ
3,CCC
4,DDD
Output:
Georgioss-MacBook-Pro:~ gsamaras$ g++ -Wall -std=c++0x main.cpp
Georgioss-MacBook-Pro:~ gsamaras$ ./a.out
ID = 1, name = NYC
ID = 2, name = ABQ
ID = 3, name = CCC
ID = 4, name = DDD