Not able to read data from text file and convert it to integer

Hi,

I am trying to read an array values from Tmin.txt file. I take array size from user viz. number of raw & column and then, read the following data from Tmin.txt file which look like this:

20 40 20 25 30

20 30 40 20 25

20 40 20 25 30

20 30 40 20 25

30 40 40 30 40

i am using getline, and then converting it to int by using atoi. But my code is not working. can somebody help me out on this.

Code :

Code:

---

// reading a text file
#include <iostream>
#include <fstream>
#include <string>


using namespace std;


int main () {


 string line;
 int i,j,c;
 int Ncoil, Ntank;
 int **Tmin;
 string **Tminstring;
 char str[256];


 cout << "Number of coils to be cleaned: ";
 cin >> Ncoil;


 cout << "Number of tanks: ";
 cin >> Ntank;


Tmin = new int *[Ncoil];


 for (int i = 0; i <= Ncoil; ++i)
    {
        Tmin[i] = new int[Ntank];
        for(int j = 0; j <= Ntank; ++j)
            {
            ifstream myfile ("Tmin.txt");
                if (myfile.is_open())
                {
                    while ( myfile.good() )
                        {
                            getline(myfile, line, ' ');
                            c = atoi(line);
                            Tmin[i][j] = c;
                            myfile.close();
                        }
                }
                else cout << "Unable to open output file";
            }
    }
  return 0;
}

---

For starters, change your code to make use of std::vector or some other suitable container instead of performing manual memory management.

Next, open the file once, not on each iteration of the loop. Then, use the return value of getline, not good(), to control the inner loop.

In the inner loop, since the line has more than one integer, yet it is a known number of them, initialise a stringstream with the line, then use operator>> to extract the integers.

First, you need to include the standard library as atoi is defined within the stdlib: #include <stdlib.h>

Secondly, I believe the atoi function works on C style strings which are character array's and not C++ style string class. Because of this, add in line 44 a conversion from your C++ string class to a c style string using the c_str() function. Then pass that converted string, called cstr, to the atoi function. In other words, cstr (converted C character array) = line (C++ string instance).

Below compiles fine (added in comments where changed):

Code:

---

// reading a text file
#include <iostream>
#include <fstream>
#include <string>
#include <stdlib.h>    /* ADD THIS DEFINE */


using namespace std;


int main () {


 string line;
 int i,j,c;
 int Ncoil, Ntank;
 int **Tmin;
 string **Tminstring;
 char str[256];


 cout << "Number of coils to be cleaned: ";
 cin >> Ncoil;


 cout << "Number of tanks: ";
 cin >> Ntank;


Tmin = new int *[Ncoil];


 for (int i = 0; i <= Ncoil; ++i)
    {
        Tmin[i] = new int[Ntank];
        for(int j = 0; j <= Ntank; ++j)
            {
            ifstream myfile ("Tmin.txt");
                if (myfile.is_open())
                {
                    while ( myfile.good() )
                        {
                            getline(myfile, line, ' ');
                            char * cstr = new char [line.length()+1];              /* CONVERT C++ STRING TO C CHAR ARRAY */
                            c = atoi(cstr);                                                        /* AND PASS THIS C CHAR ARRAY TO ATOI */
                            Tmin[i][j] = c;
                            myfile.close();
                        }
                }
                else cout << "Unable to open output file";
            }
    }
  return 0;
}

---

The question now is; does it do what you want it to do.

Quote:

---

Originally Posted by Vespasian

Below compiles fine:

---

"Compiles" and "works correctly" are not necessarily the same thing.

Quote:

---

Originally Posted by laserlight

"Compiles" and "works correctly" are not necessarily the same thing.

---

Yeah I edited the post just after posting:

Quote:

---

The question now is; does it do what you want it to do.

---

> for (int i = 0; i <= Ncoil; ++i)
> for(int j = 0; j <= Ntank; ++j)
Repeat after me - this is a buffer overrun

If you've got N of something, then you loop from 0 to N-1, which is conveniently written as
for ( i = 0 ; i < N ; i++ )

Thanks all! it was really helpful. I am a noob.

@laserlight : I have changed my code as follows, but i don't know how do this -->

Quote:

---

Then, use the return value of getline, not good(), to control the inner loop.

---

can you explain me in more details.

New code:

Code:

---

// reading a text file
#include <iostream>
#include <fstream>
#include <string>

using namespace std;

int main () {

 string line;
 int i,j,c;
 int Ncoil, Ntank;
 int **Tmin, **Tmax;
 
 char str[256];

 cout << "Number of coils to be cleaned: ";
 cin >> Ncoil;

 cout << "Number of tanks: ";
 cin >> Ntank;

Tmin = new int *[Ncoil];
ifstream myfile ("Tmin.txt");
if (myfile.is_open())
    {
       
            for (int i = 0; i <= Ncoil; ++i)
              {
                Tmin[i] = new int[Ntank];
                for(int j = 0; j <= Ntank; ++j)
                    {
                            getline(myfile, line, ' ');
                            while (???????)
                            {
                            c = atoi(line.c_str());
                            Tmin[i][j] = c;
                            cout<< Tmin[i][j]<<endl;
                            }
                    }
                   
            }
            myfile.close();
    }

else cout << "Unable to open Tmin file";
   
     
 
  return 0;
}

---

Finally this one is working, thanks all. :redface:

I have one more question. Should I free the memory space and how?

Code:

---

// reading a text file
#include <iostream>
#include <fstream>
#include <string>

using namespace std;

int main () {

 string line;
 int i,j,c;
 int Ncoil, Ntank;
 int **Tmin, **Tmax;
 
 char str[256];

 cout << "Number of coils to be cleaned: ";
 cin >> Ncoil;

 cout << "Number of tanks: ";
 cin >> Ntank;

Tmin = new int *[Ncoil];
ifstream myfile ("Tmin.txt");
if (myfile.is_open())
    {
        do{
            for (int i = 0; i < Ncoil; ++i)
              {
                Tmin[i] = new int[Ntank];
                for(int j = 0; j < Ntank; ++j)
                    {
                        myfile >> Tmin[i][j];
                            /*getline(myfile, line, ' ');
                            c = atoi(line.c_str());
                            Tmin[i][j] = c;
                            cout<< Tmin[i][j]<<endl; */
                        cout << Tmin[i][j]<<' ';
                            }
                    }
                   
            }while(!myfile.eof());
    myfile.close();
    }
         
   

else cout << "Unable to open Tmin file";
       
 cin.get();       
 
  return 0;
}

---

Quote:

---

Originally Posted by pratras

Finally this one is working, thanks all. :redface:

I have one more question. Should I free the memory space and how?

---

Use a container, eg std::vector. Then you don't have to free.
For example (2d array):

std::vector<std::vector<T>> v(N, std::vector(M));
<==>
T v[N][M];

where N and M are dynamic, ie can be variables.

Quote:

---

Originally Posted by Elysia

Use a container, eg std::vector. Then you don't have to free.
For example (2d array):

std::vector<std::vector<T>> v(N, std::vector(M));
<==>
T v[N][M];

where N and M are dynamic, ie can be variables.

---

can you please elaborate how i can use vector in my case, i didn't get
"std::vector<std::vector<T>> v(N, std::vector(M));" this line..

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