Open and read from a file c++

We can then perform the same operations on these streams as on cin and cout: operators >> and <<, getlinefunction, ...

There are four methods to check the status of a stream at any time:

• eof(): in read mode, when the end of a file is encountered ;
• fail(): logical error while reading or writing ;
• bad(): system error which reading or writing ;
• good(): all is ok ;

and two methods to manage the status of a file :

• bool is_open() checks that the stream is open;
• void close() closes the stream (obligatory at the end of each use).

Examples

Writing a sequence of integers in a file:

int main()
{
   string fileName;
   ofstream output;

    vector<int> v = {1,2,40,5,7,8,10};

    try {
       cout << "Name of file to create?";
       cin >> fileName;
       output.open(fileName);
       if(!(output.is_open())) throw(fileName);
       output << v.size() << endl;
       for(int i=0; i<v.size(); i++)

           output << v[i] << ' ' ; // do not forget to include a separator
       output << endl;
       output.close();
   } catch (string s) {
       cerr<< "Problem encountered while opening file: " << fileName;
   }

    return 0;
}

Reading a sequence of integers from a file:

int main()
{
   string fileName;
   ifstream input;

    vector<int> v(0);

    try {
       cout << "Name of file to read?";
       cin >> fileName;
       input.open(fileName);
       if(!(input.is_open())) throw(fileName);
       int nbInt;
       if (!input.eof())
           input >> nbInt;
       for (int i = 0; i < nbInt && !input.eof(); i++) {
           int val;
           input >> val;
           v.push_back(val);
       }
       input.close();
       cout << "We have read:";
       for (int i = 0; i < v.size(); i++) {
           cout << " " << v[i];
       }
       cout << endl;
   } catch (string s) {
       cerr<< "Problem encountered while opening file : " << fileName;
   }

    return 0;
}

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