Dynamic Arrays

[KatieK]

Hello I'm not that familiar with Dynamic Arrays, I need to create one that is of type class, that reads data from a file, I've gotten up to the point where I've allocated the array to the appropriate size but I just don't know how to read data from a file into the array. In the interest of space I have only included parts of the code:


<Problem *problems;//created in class file as private data member>

<ProblemSet::ProblemSet(istream& is)
{
problems = new Problem[n];

countEntries(is);
for(int i=0; i<n; i++)
{
problems[n]=//need to read in data from file here
}

}>

Any suggesions/help would be greatly appreciated as I don't really understand how dynamic arrays are initialized.
Thanks!

[misplaced]

lookup <fstream>

namely:
ofstream and ifstream

btw: use code tags...read the forum sticky

[hk_mp5kpdw]

What data are you trying to read from the file? Is it binary data or text? What does a "line" of input look like and how does it relate to the Problem objects you are attempting to store? What does a Problem object look like?

Basic file input can be done with an ifstream (input file stream) object. For text data (whitespace delimited) you would typically use the extraction operator >> just like you would use to get input from the user when using cin. The following example will read/count words (whitespace delimited) from the file specified while outputing the count/word to the console.

#include <fstream>
#include <string>
#include <iostream>
using namespace std;

int main()
{
    ifstream input("file.txt");  // Try to open a file named file.txt
    string str;
    int count = 0;

    if( input.is_open() )        // Check if file was opened
    {
        cout << "File successfully opened." << endl;
        while( input >> str )    // while there is data to get from file...
        {
            ++count;
            cout << "Word " << count << " is: " << str << endl;
        }
        cout << "There were " << count << " words in total." << endl;
    }
    else
    {
        cout << "Could not open file." << endl;
    }

}

The destructor for the ifstream object will close the file automatically for you. Without knowing how your data looks in the file and how it translates into a Problem object it is impossible to know exactly what you need.