CBSE Class 12 Computer Science Data File Handling In C++ Concepts

DATA FILE HANDLING IN C++

File

• A file is a stream of bytes stored on some secondary storage devices.

• Text file: A text file stores information in readable and printable form. Each line of text is terminated with an EOL (End of Line) character.

• Binary file: A binary file contains information in the non-readable form i.e. in the same format in which it is held in memory.

File Stream

• Stream: A stream is a general term used to name flow of data. Different streams are used to represent different kinds of data flow.

• There are three file I/O classes used for file read / write operations.

• ifstream - can be used for read operations.

• ofstream - can be used for write operations.

•  fstream - can be used for both read & write operations.

File modes:

• ios::out It open file in output mode (i.e write mode) and place the file pointer in beginning, if file already exist it will overwrite the file.

• ios::in It open file in input mode(read mode) and permit reading from the file.

• ios::app It open the file in write mode, and place file pointer at the end of file i.e to add new contents and retains previous contents. If file does not exist it will create a new file.

• ios::ate It open the file in write or read mode, and place file pointer at the end of file i.e input/ output operations can performed anywhere in the file.

• ios::trunc It truncates the existing file (empties the file).

• ios::nocreate If file does not exist this file mode ensures that no file is created and open() fails.

• ios::noreplace If file does not exist, a new file gets created but if the file already exists, the open() fails.

• ios::binary Opens a file in binary mode.

eof(): This function determines the end-of-file by returning true(non-zero) for end of file
otherwise returning false(zero).

close(): This function terminates the connection between the file and stream associated with it.

Stream_object.close(); e.g file.close();

Text File functions:

Char I/O :

· get() – read a single character from text file and store in a buffer.
e.g file.get(ch);

· put() - writing a single character in textfile e.g. file.put(ch);

· getline() - read a line of text from text file store in a buffer.
e.g file.getline(s,80);

· We can also use file>>ch for reading and file<<ch writing in text file. But >> operator
does not accept white spaces.

Binary file functions:

· read()- read a block of binary data or reads a fixed number of bytes from the specified

stream and store in a buffer.

Syntax : Stream_object.read((char *)& Object, sizeof(Object));
e.g file.read((char *)&s, sizeof(s));

· write() – write a block of binary data or writes fixed number of bytes from a specific
memory location to the specified stream.

Syntax : Stream_object.write((char *)& Object, sizeof(Object));
e.g file.write((char *)&s, sizeof(s));

Note:

Both functions take two arguments.

• The first is the address of variable, and the second is the length of that variable in bytes. The address of variable must be type cast to type char*(pointer to character type)

• The data written to a file using write( ) can only be read accurately using read( ).

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