File Streams & String Streams - C++ Programming Questions and Answers

This section on C++ interview questions and answers focuses on “File Streams and String Streams”. One shall practice these interview questions to improve their C++ programming skills needed for various interviews (campus interviews, walkin interviews, company interviews), placements, entrance exams and other competitive exams. These questions can be attempted by anyone focusing on learning C++ programming language. They can be a beginner, fresher, engineering graduate or an experienced IT professional. Our C++ interview questions come with detailed explanation of the answers which helps in better understanding of C++ concepts.

Here is a listing of C++ interview questions on “File Streams and String Streams” along with answers, explanations and/or solutions:

1. Which operator is used to insert the data into file?
a) >>
b) <<
c) <
d) >
View Answer

Answer: b
Explanation: You can write information to a file from your program using the stream insertion operator <<.

2. Which function is used to position back from the end of file object?
a) seekg
b) seekp
c) both seekg & seekp
d) seekf
View Answer

Answer: a
Explanation: The member function seekg is used to position back from the end of file object.

3. How many objects are used for input and output to a string?
a) 1
b) 2
c) 3
d) 4
View Answer

Answer: c
Explanation: The stringstream, ostringstream, and istringstream objects are used for input and output to a string.

4. What will be the output of the following C++ code?

```
    #include <iostream>
```
```
    #include <fstream>
```
```
    using namespace std;
```
```
    int main () 
```
```
    {
```
```
        int length;
```
```
        char * buffer;
```
```
        ifstream is;
```

        is.open ("sample.txt", ios :: binary );

```
        is.seekg (0, ios :: end);
```
```
        length = is.tellg();
```
```
        is.seekg (0, ios :: beg);
```
```
        buffer = new char [length];
```
```
        is.read (buffer, length);
```
```
        is.close();
```
```
        cout.write (buffer, length);
```
```
        delete[] buffer;
```
```
        return 0;
```
```
    }
```

a) This is sample
b) sample
c) Error
d) Runtime error
View Answer

Answer: d
Explanation: In this program, if the file exist, it will read the file. Otherwise it will throw an exception. A runtime error will occur because the value of the length variable will be “-1” if file doesn’t exist and in line 13 we are trying to allocate an array of size “-1”.

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5. What will be the output of the following C++ code?

```
    #include <iostream>
```
```
    using namespace std;
```
```
    int main ()
```
```
    {
```
```
        char first, second;
```
```
        cout << "Enter a word: ";
```
```
        first = cin.get();
```
```
        cin.sync();
```
```
        second = cin.get();
```
```
        cout << first << endl;
```
```
        cout << second << endl;
```
```
        return 0;
```
```
    }
```

a) first
b) second
c) returns first 2 letter or number from the entered word
d) third
View Answer

Answer: c
Explanation: In this program, We are using the sync function to return the first two letters of the entered word.
Output:

$ g++ stream.cpp
$ a.out
Enter a word: steve
s
t

6. What will be the output of the following C++ code?

```
    #include<iostream>
```
```
    #include <fstream>
```
```
    using namespace std;
```
```
    int main () 
```
```
    {
```
```
        ofstream outfile ("test.txt");
```
```
        for (int n = 0; n < 100; n++)
```
```
        {
```
```
            outfile << n;
```
```
            outfile.flush();
```
```
        }
```
```
        cout << "Done";
```
```
        outfile.close();
```
```
        return 0;
```
```
    }
```

a) Done
b) Error
c) Runtime error
d) DoneDoneDone
View Answer

Answer: a
Explanation: In this program, We are using the flush function to update the contents in a file.
Output:

$ g++ stream1.cpp
$ a.out
Done

7. What will be the output of the following C++ code?

```
    #include <iostream>
```
```
    using namespace std;
```
```
    int main ()
```
```
    {
```
```
        int a = 100;
```
```
        double b = 3.14;
```
```
        cout << a;
```
```
        cout << endl;
```
```
        cout << b << endl << a * b;
```
```
        endl (cout);
```
```
        return 0;
```
```
    }
```

a) 100
b) 3.14
c) 314
d) All of the mentioned
View Answer

Answer: d
Explanation: In this program, We are printing the given value and manipulating the given value by using endl.
Output:

$ g++ stream2.cpp
$ a.out
100
3.14
314

8. By seeing which operator thus this C++ program stops getting the input?

```
    #include <iostream>
```
```
    #include <fstream>
```
```
    using namespace std;
```
```
    int main ()
```
```
    {
```
```
        char ch;
```
```
        streambuf * p;
```
```
        ofstream os ("test.txt");
```
```
        pbuf = os.rdbuf();
```
```
        do {
```
```
            ch = cin.get();
```
```
            p -> sputc(ch);
```
```
        } while (ch != '.');
```
```
        os.close();
```
```
        return 0;
```
```
    }
```

a) dot operator
b) insertion operator
c) $ symbol
d) @ symbol
View Answer

Answer: a
Explanation: This program will stop getting the input, When it occurs the dot(.) operator.
Output:

$ g++ stream3.cpp
$ a.out
Steve.

9. Which member function is used to determine whether the stream object is currently associated with a file?
a) is_open
b) buf
c) string
d) is_out
View Answer

Answer: a
Explanation: The member function is_open can be used to determine whether the stream object is currently associated with a file.

10. Which header file is used for reading and writing to a file?
a) #include<iostream>
b) #include<fstream>
c) #include<file>
d) #include<fe>
View Answer

Answer: b
Explanation: <fstream> header file contains all the file reading and writing functions. Also <ifstream> and <ofstream> contains functions only reading and only writing to files related functions respectively.

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