To store tokens into an array

Question

A novice at C++, i am trying to create a stats program to practice coding. i am hoping to get a text file, read it and store values into arrays on which i can perform mathematical operations. i am stuck here

 main ()
 {
      char output[100];
      char *charptr;
      int age[100];
      ifstream inFile;
      inFile.open("data.txt");
      if(!inFile)
      {
            cout<<"didn't work";
            cin.get();
            exit (1);
      }

      inFile.getline(output,100);
      charptr = strtok(output," ");
      for (int x=0;x<105;x++)
      {
           age[x] = atoi(charptr);
           cout<<*age<<endl;

      }

     cin.get();
}

in the code above, I am trying to store subject ages into the int array 'age', keeping ages in the first line of the file. I intend to use strtok as mentioned, but i am unable to convert the tokens into the array.

As you can obviously see, I am a complete noob please bear with me as I am learning this on my own. :)

Thanks

P.S: I have read similar threads but am unable to follow the detailed code given there.

I'd recommend you look into using std::vector for doing this — shuttle87, Feb 13 '12 at 15:22
The same problem exactly was discussed not far along: http://stackoverflow.com/questions/9241449/read-files-by-character-c/9241472 — Lol4t0, Feb 13 '12 at 15:23
"output" is a weird name for the input to a program. Proper naming is a good habit to get into even as you start learning. — molbdnilo, Feb 13 '12 at 16:44

score 5 · Accepted Answer · answered Feb 13 '12 at 15:43

There are a few issues with the for loop:

Possibility of going out-of-bounds due to age having 100 elements, but terminating condition in for loop is x < 105
No check on charptr being NULL prior to use
No subsequent call to strtok() inside for loop
Printing of age elements is incorrect

The following would be example fix of the for loop:

charptr = strtok(output, " ");
int x = 0;
while (charptr && x < sizeof(age)/sizeof(age[0]))
{
    age[x] = atoi(charptr);
    cout << age[x] << endl;
    charptr = strtok(NULL, " ");
    x++;
}

As this is C++, suggest:

using std::vector<int> instead of a fixed size array
use the std::getline() to avoid specifying a fixed size buffer for reading a line
use std::copy() with istream_iterator for parsing the line of integers

For example:

#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <vector>
#include <algorithm>
#include <iterator>

int main ()
{
    std::vector<int> ages;
    std::ifstream inFile;
    inFile.open("data.txt");
    if(!inFile)
    {
        std::cout<<"didn't work";
        std::cin.get();
        exit (1);
    }

    std::string line;
    std::getline(inFile, line);

    std::istringstream in(line);

    std::copy(std::istream_iterator<int>(in),
              std::istream_iterator<int>(),
              std::back_inserter(ages));

    return 0;
}

Thanks hmjd. i'm 'practising vectors ' right now lol as my course notes didnt cover them. will get to trying out your solution soon. many thanks. btw i am reading dietel & dietel (too lengthy). — Alter Ego, Feb 13 '12 at 15:53

To store tokens into an array

1 Answers1