in the output why the letter 'e' of welcome is repeated?

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When i execute the below program on giving a string as a 'welcome' , then the 'welcomee' is displayed instead of 'welcome' . in the output why the letter 'e' of welcome is repeated?

C++

int main()
{
    char ch[10],c;
    fstream f;
    f.open("text",ios::out);
    cout<<"Enter a string :";
    cin>>ch;
    f<<ch;
    f.close();
    
    f.open("text",ios::in);
    while(f)
    {
            f.get(c);
            cout<<c;
    }
    f.close();
    getch();
    return 0;
}

Posted 15-Mar-12 6:28am

Ashutosh_g

Updated 15-Mar-12 6:55am

Jochen Arndt

v2

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Sergey Alexandrovich Kryukov 15-Mar-12 14:18pm

Why not using std::string instead those brain-damaging null-terminated strings, once you already use std?
--SA

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Emilio Garavaglia · Answer 1 · 2012-03-15T22:11:00

What happens if at cin>>ch the user types more than 9 characters?
What happens if the user type some spaces ?

If you want to use fixed buffers and null-terminates C strings, you have always to take care of the space and of the null-termination.
Also, to "pause at the and", yopu must ensure that no unread input is present.
The way to do that is discard every residual input after the read of the string.

C++

#include <iostream>
#include <fstream>
#include <iomanip>
#include <cstring>
#include <limits>

int main()
{
    using namespace std;

    const unsigned BUFFSZ=9;
    char ch[BUFFSZ+1];
    memset(ch,0,sizeof(char)*(BUFFSZ+1));
    char c=0;

    fstream f;
    f.open("text",f.out);
    cout<<"Enter a string :";
    // read up to BUFSZ chars
    cin >> std::setw(BUFFSZ) >> ch;
    //discard exceeded input up to the end of line
    cin.ignore(numeric_limits<streamsize>::max(),'\n');

    f<<ch;
    f.close();


    f.open("text",f.in);
    while(f.get(c))
    {
        cout<<c;
    }
    f.close();

    cin.get(); //pause

    return 0;
}

The above program is safe, but reads the string up to the first space and up to 9 character (note the ch is 9+1 since there must be the space for the null character string terminator.

Note that f.get(c) is used in the loop condition: in your original loop, when you read the last character with f.get(c), the file is still "good", so you make another turn, f.get(c) fails, (making the file bad)and c is left the the previous character (hence the repetition in printing)

If you want to be more safe, you should use std::string that uses dynamic memory to accommodate whatever length:

C++

#include <iostream>
#include <fstream>
#include <string>
#include <limits>

int main()
{
    using namespace std;
    string ch; //no more an array
    char c=0;

    fstream f;
    f.open("text",f.out);
    cout<<"Enter a string :";
    getline(cin, ch);

    f<<ch;
    f.close();

    f.open("text",f.in);
    while(f.get(c))
    {
        cout<<c;
    }
    f.close();

    cin.get(); //pause

    return 0;
}

There is no more need to take care about the length, the entered text can contain spaces and the line is read to the end (so no cleanup is required).

#realJSOP · Answer 2 · 2012-03-15T07:03:00

Solution 2

If you run it under the debugger, you'll see why.

Posted 15-Mar-12 7:03am

#realJSOP

enhzflep · Answer 3 · 2012-03-15T07:12:00

Solution 3

That's because the last time through the loop, f.get(c) doesn't return any new data.

To see what I mean, simply set c = 0x0 right before you retrieve each char. When done, the last letter is not repeated.

Posted 15-Mar-12 7:12am

enhzflep

User 59241 · Answer 4 · 2012-03-15T16:41:00

Using tip in solution #3

C#

int main()
{
    char ch[10],c;
    fstream f;
    f.open("text",ios::out);
    cout<<"Enter a string :";
    cin>>ch;
    f<<ch;
    f.close();

    f.open("text",ios::in);

    while(f.good())
    {
            // When last character has been read the loop is still valid and gets to here.
            f.get(c);

            // Now we may have read past last character so check it before making boo-boo. 
            if(f.good())
             cout<<c;
    }
    f.close();
    getch();
    return 0;
}

JackDingler · Answer 5 · 2012-03-15T07:02:00

Solution 1

Shouldn't that while statement read,

C++

while(f.good())

?

Posted 15-Mar-12 7:02am

JackDingler

Comments

enhzflep 15-Mar-12 14:46pm

Nope.
Doesn't help.