Creating variables using input from a file [duplicate]

Question

I hope somebody can help me.

I have a file with a list of lots of cities that can be repeated. For example:

Lima, Peru

Rome, Italy

Madrid, Spain

Lima, Peru

I have created a class City with a constructor City( string cityName )

In the main, I want to create a pointer with each city, like:

City* lima = new City( City("Lima, Peru"); 

City* rome = new City( City("Rome, Italy");

is there a way to do this with a loop reading lines from the text, like:

City* cities = new City[];
int i = 0;
while( Not end of the file )
{
   if( read line from the file hasn't been read before )
     cities[i] =  City(read line from the file);   
}

Is there a way, or I have to do it manually for each one. Any suggestions?

Thanks

Not an answer, but there is something strange about how you use constructors. To create a City object dynamically, best use City *lima = new City("Lima, Peru");, not City *lima = new City(City("Lima, Peru"));. — jogojapan
– jogojapan, Commented May 27, 2013 at 1:53
See here: stackoverflow.com/questions/7143120/…, stackoverflow.com/questions/8641751/…, stackoverflow.com/questions/11183429/… — jogojapan
– jogojapan, Commented May 27, 2013 at 2:01

Tony Delroy · Accepted Answer · 2013-05-27 02:08:45Z

1

Because you want to list cities just once, but they might appear many times in the file, it makes sense to use a set or unordered_set so that insert only works the first time....

std::set<City> cities;
if (std::ifstream in("cities.txt"))
    for (std::string line; getline(in, line); )
        cities.insert(City(line));  // fails if city already known - who cares?
else
    std::cerr << "unable to open input file\n";

answered May 27, 2013 at 2:08

Tony Delroy

107k16 gold badges188 silver badges265 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

user2419831 Over a year ago

Thanks everybody and thanks Tony . I get it now, I will use a set since I don't want cities to ne repeated ....you guys are very helpful. Thanks a lot

Tony Delroy Over a year ago

@user2419831: one thing - you'll need a bool operator<(const City& rhs) { ... } function in your City class to tell std::set how to compare Citys - it can probably just return city_name_ < rhs.city_name_; where city_name_ is whatever you've called the data member with that meaning.

David G · Accepted Answer · 2013-05-27 02:13:32Z

0

You should use a std::vector of City objects to store the instances. And getline should suffice for this situation:

std::vector<City> v;
std::fstream out("out.txt"); // your txt file

for (std::string str; std::getline(out, str);)
{
    v.push_back(City(str));
}

edited May 27, 2013 at 2:13

answered May 27, 2013 at 1:44

David G

97.6k41 gold badges173 silver badges258 bronze badges

3 Comments

Tony Delroy Over a year ago

What potential use would reflection be for this requirement?

David G Over a year ago

@TonyD I'm thinking he's asking to make a variable name by the text inside the file.

Tony Delroy Over a year ago

Ahh yes - "City* lima = ..." - thanks - I'd not paid attention to that.

Collectives™ on Stack Overflow

Creating variables using input from a file [duplicate]

2 Answers 2

2 Comments

3 Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

3 Comments

Linked

Related