CODEWITHSUNDEEP
c++arraysfilereader
Mark Young
Mark Young

Reputation: 39

How to read from a text file and adding to array in c++

How would I go about reading numbers from a text file and adding them to an array?

textfile: HEAPinput2.txt

12
9
10
11
12
2
4
6
5
3
1
7
8

What I have here is a snippet of my code. If needed I will provide my whole main. But essentially I have a switch statement, when user chooses R read from a file and sort them into the array. I've been looking online and have been seeing different ways of doing it, I have done it as shown below, but have been running into some errors 

case 'R':
file.open("<path of HEAPinput>");
if(!file){
        cout<<"There was a problem opening file HEAPinput2.txt for reading";
        exit(0);
 }
else{
        int count = 0;
        std:: int count;
        while(file>>count){
                    count++; //making sure it increments the
        }
        elme = *new ELEMENT[count];
        cout<<count; //prints out 8 for some reason
    }
    break;

Upvotes: 0

Views: 1023

Answers (2)

Christophe
Christophe

Reputation: 73637

Assuming that the first integer of the text file is the number of remaining integers to be read, and that elme is an int*, and that you are not allowed for this exercise to use vectors: 

else{
    int count = 0;    // this should REALLY be declared in same block as elme
    int i=0; 
    if(file>>count) {  
        elme = new int[count];   // assuming that count is valid and not 0
        while (i<count && file>>elme[i]) 
            i++;   
        count = i; //  to adjust the number of items to the number really read
    }
    cout<<count; 
}
break;

If you're allowed to use vectors, then go to Paul Sander's answer because vector is really century XXI for C++, whereas dynamically allocated arrays are something like the medieval age.

Upvotes: 0

catnip
catnip

Reputation: 25418

To sum up what others have said, this is extremely easy with std::vector:

#include <vector>
#include <fstream>
#include <iostream>

int main ()
{
    std::ifstream file;
    file.open ("<path of HEAPinput>");
    if(!file)
    {
        std::cout << "There was a problem opening file HEAPinput2.txt for reading";
        exit (0);
    }

    std::vector <int> v;
    int i;
    while (file >> i)
        v.push_back (i);
    file.close ();
}

More details on std::vector here:

https://en.cppreference.com/w/cpp/container/vector

Upvotes: 1

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