IO Systems and File IO: Two Marks Important Questions and Answers

Object Oriented Programming – C++

Chapter 6: IO Systems and File IO

Two Marks Questions with Answers

1. What is stream?

Answer: Stream is a channel on which data flow from sender to receiver. Data can be sent out from the program in an output stream or received into the program in an input stream. A stream is connected to a physical device by the C++ input output system. Examples: The cin is a standard input stream and cout is a standard output stream.

2. Enlist the libraries used in handling the stream operations.

Answer:Following are the standard header files used for handling the stream operations

a. iostream.h

b. iomanip.h

c. strstream.h

d. fstream.h

3. What is formatted I/O ?

Answer: Each stream is associated with a set of format flags that control the way information is formatted. The ios class declares the values that are used to set or clear the format flags. Some format flags are

Flags: Meaning

skipws: If this flag is set then leading white spaces are discarded(skipped). On clearing this flag the leading white spaces are not discarded.

left: On setting this flag the output becomes left justified.

right: On setting this flag the output becomes right justified.

scientific: On set it shows exponential format on floating point numbers

fixed: On set it shows fixed format on floating point numbers.

uppercase: On setting this flag upper case A‒F are used for hex values and E for scientific values.

4. How can you create a file in the append mode?

Answer: The ios::app mode is used for opening the file in append mode. The code for this is

ofstream fp; //creating a file object for writing to the file.

fp.open("output.dat",ios::app)

5. What is file mode ? List any four file modes.

Answer: File mode is a specification which denotes the manner by which the file is to be opened. Various file modes are

Ios::in: Open for input operation.

Ios::out: Open for output operation.

Ios::binary: Open for binary operations.

6. Give the purpose of gets and puts function.

Answer: The gets(char *str) is used for reading the string. The puts(char *str) is for displaying the string as an output. In other words gets is for reading the string and the puts is for writing the string.

7. List down the functions of manipulators.

Answer: Following table shows some commonly used functions of manipulators

Function      :    Meaning

showbase    ‒   Shows numerical base prefix

showpoint  ‒    Shows decimal point

uppercase  ‒    Converts to upper case letters

skipw         ‒    Skips whitespaces

endl            ‒     Inserts newline.

setw            ‒      Sets the field width

8. What are manipulators? Give any two examples.

Answer: Manipulators are the operators in C++ that are used for formatting the output. Various commonly used manipulators are setw, endl and setfill.

The setw is used to set the minimum field width. For example ‒ setw(30) will set the right justified numbers

The endl is similar to a newline character.

9. Give the meaning of the flag ios::out.

Answer: The flag ios::out is used for opening a file for output operation.

10. Explain the seek operation used in file.

Answer: The seek operation is used to reach to any desired position inside the file. There are two commonly used functions associated with seek‒

a. seekg ‒ Means get pointer of specific location for reading of the record.

b. seekp ‒ Means get pointer of specific location for writing of the record.

The syntax for the seekg and seekp operations is

seekg(offset,reference‒position);

seekp(offset,reference‒position);

11. Explain the tell function.

Answer: The tell function is used to tell the current position in the file.

For example:

seqfile.tellg() ‒ returns the current position of get pointer(for reading the record)

seqfile.tellp() returns the current position of put pointer(for writing the record)