Read & Write file into array

Question

I am trying to write to a text file and read from text file to get the average score of items in an array. Here is my code:

#include <iostream>
#include <fstream>

using namespace std;

int main()
{
float total =0;;

ofstream out_file;
out_file.open("number.txt");

const int size = 5;
double num_array[] = {1,2,3,4,5}; 

for (int count = 0; count < size; count++)
{
    if (num_array[count] == 0)
    {
        cout << "0 digit detected. " << endl;
        system("PAUSE");
    }
}
double* a = num_array;
out_file << &a;

out_file.close();

ifstream in_file;
in_file.open("number.txt");
if(in_file.fail())
{
    cout << "File opening error" << endl;
}else{
    for (int count =0; count< size; count++){
        total += *a;  // Access the element a currently points to
        *a++;  // Move the pointer by one position forward
    }
}

cout << total/size << endl;

system("PAUSE");
return 0;
}

However, this program just simply execute without reading from a file and return the correct average score. And this is what I get in my text file :

0035FDE8

I thought it supposed to write the entire array into text file, and from there I retrieve the elements and calculate for the average?

Edited Portion

I have fixed the writing to text file part using a for loop on pointer :

for(int count = 0; count < size; count ++){
    out_file << *a++ << " " ;
}

But now I having another problem which is I cannot read the file and compute for the average. Anybody know how to fix?

You are seeing the address of a pointer in the file and is coming because of the statement out_file << &a;. — Mahesh
– Mahesh, Commented May 15, 2013 at 13:45

user93353 · Accepted Answer · 2013-05-15 13:50:40Z

2

You are writing the address of the pointer to the array into the file, not the array itself.

out_file << &a;

Hence you get 0035FDE8 in the file which is an address.

You can write each value into the file by using out_file<<num_array[count] in a for loop. You will also have read using a similar for loop.

edited May 15, 2013 at 13:50

answered May 15, 2013 at 13:44

user93353

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4 Comments

Mahesh Over a year ago

@Yvonne You have to write each element in to the file by accessing it's actual value with index operator. out_file << a[0] << " " << a[1];

Yvonne Over a year ago

I used a for loop, for example : for(int count = 0; count < size; count ++){ out_file << *a++ << " " ; } and it's fixed. But there's another problem, the program does not read from the file

user93353 Over a year ago

@Yvonne - if you are writing in a loop, you also have to read in a loop.

Yvonne Over a year ago

@user93353 mind to give me some example? How can I read from loop and store it as variable total?

praks411 · Accepted Answer · 2013-05-15 14:05:10Z

1

You can try something like this

double total =0;

    std::ofstream out_file;
    out_file.open("number.txt");

    const int size = 5;
    double num_array[] = {1,2,3,4,5}; 

    for (int count = 0; count < size; count++)
    {
        if (num_array[count] == 0)
        {
            std::cout << "0 digit detected. " << std::endl;
            system("PAUSE");
        }
        else
        {
            out_file<< num_array[count]<<" ";    
        }
    }
    out_file<<std::endl;
    out_file.close();
    std::ifstream in_file;
    in_file.open("number.txt");
    double a;
    if(in_file.fail())
    {
        std::cout << "File opening error" << std::endl;
    }
    else
    {
        for (int count =0; count< size; count++)
        {
            in_file >> a;
            total += a;  // Access the element a currently points to
        }
    }

        std::cout << total/size << std::endl;

answered May 15, 2013 at 14:05

praks411

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2 Comments

Yvonne Over a year ago

It works. Thanks a lot. So basically I can done this without pointer?

praks411 Over a year ago

Yes it can be done without using pointer. So simply read the numbers one at a time.

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