Files

• A file is an external collection of related data treated as a unit.

• The primary purpose of a file is to keep a record of data

• Files are required to store data in more permanent form since the contents of primary
memory are lost when the computer is shut down.

• Files are stored in auxiliary secondary storage devices.

• Two most common forms of secondary storages are:

1. (hard disk, CD and DVD)

2. Tape

Buffer:

• A temporary storage area that holds data as the computer transfers them to/from
memory.

• The primary purpose of a buffer is to synchronize the physical devices (disk,tape) with a
program’s requirement

• The buffer also holds data until it is efficient to write that data on to the storage device.

Filename

• File name is used to read or write auxiliary storage file.

• Every operating system uses a set of rules for naming its file.

Example

abc.txt, xyz.doc etc.

File information table

• A program to read or write file needs to know several pieces of information such as
operating system name, the position of current character and so on.

• C uses a structure called FILE (defined in stdio.h) to store the attributes of a file.

Stream file processing

• A stream is an entity created by the program.

• To use a file in the program, the program’s stream name must be associated with the
operating system’s file name.

• Four steps to processing a file

1. Create the stream

2. Open the which associates the stream name with the file name

3. Process file (read or write data)

4. Close the file

Creating a Stream

• A stream is created when declared.

• To declare a stream, use the FILE type

• FILE type is structure that contains information for reading and writing a file

Syntax:

FILE *ptr;

Opening a file

• Once a stream has been created, it can be associated to a file.

• The standard open function can be used to open the file.

• The file open function returns address of the file type, which is stored in the stream
pointer variable (*ptr).

The file open function creates the stream, which can be referred to by its name.

Using the Stream Name

• The stream pointer is used in all functions that need to access the corresponding file for
input (read) or output (write)

Closing the stream :

• Close the file at the completion of file processing.

• Closing the file breaks the association between stream name and file name

• The stream is no longer available after the closing.

• Use the close function to release the file and destroy the contents of the file.

• C provides standard streams in order to communicate with a terminal

• Streams must be created and associated with their terminal devices just like files. This is
done automatically by ‘C’.

• Three stream pointers are declared and defined in the stdio.h header file.

• Stdin points to standard input stream.

• Stdout points to standard output stream.

• Stderr points to standard error stream.

Text and Binary Streams

• Data is input to and output from a stream.

• A stream can be associated with a physical device such as terminal, or with a file stored
in auxiliary memory.

• C uses two types of streams:

1) Text stream

• A text stream consists of sequence of characters divided into lines with each line
terminated by a newline character(\n)

2) Binary stream

• A binary stream consists of sequence of data values such as integer real or complex using
their memory representation.

Text and Binary File

• A file records data only in a binary format. However, a text file and a binary file are
distinguish from each other.

Text Files

• A file in which data are stored using only characters and is written using a text stream.

• Text files are read and written using input/output functions that convert the characters to
data type as show below:

Binary Files

• A Binary file is a collection of data stored in the internal format of the computer.

• Binary files are read and written using binary streams known as block input/output
functions.

• The data are stored in the file in the same format that they are stored in memory
 Creating and Reading and writing text and binary files

File open (fopen)

• The file open function (fopen) serves two purposes:

1) It makes the connection between the physical file and the file stream in the program.

2) It creates a program file structure to store the information needed to process the file.

• Syntax:
fopen(“filename”, “mode”);

• First parameter is filename and second parameter is mode

• A file name is string .the name consist of eight characters and three characters for file
extension

• Ex: 1) text.txt 2) myfile.dat 3) stud.doc

• The file mode is a string that specifies the intend to use the file.

• Example

• spData = fopen(“MYFILE.DAT”, “w”);

• spData = fopen(“A:\\MYFILE.DAT”, “w”);

File open modes

• The mode shows how to use the file: for reading, for writing or for appending.
• C has three different file modes as shown in table:
File Close (fclose)

• File should be closed when no longer required to free system resources, such as buffer
space.

• Use fclose function to close a file and the pointer variable

Syntax:
fclose(spData);

File I/O functions:

getc(), putc() functions are file handling function in C programming language which is used to
read a character from a file (getc) and display on standard output or write into a file
(putc). Please find below the description and syntax for above file handling functions.

getc()/fgetc():

Declaration: intgetc(FILE *fp)

getc functions is used to read a character from a file. In a C program, we read a character as
below.
getc (fp);

putc()/fputc()

Declaration: intputc(int char, FILE *fp)

putc function is used to display a character on standard output or is used to write into a file. In a
C program, we can use putc as below.

putc(char, stdout);
putc(char, fp);

Example:

#include <stdio.h>
int main()
{
charch;
FILE *fp;
if (fp = fopen("test.c", "r"))
{
ch = getc(fp);
while (ch != EOF)
{
 putc(ch, stdout);
ch = getc(fp);
}
fclose(fp);
return 0;
}
return 1;
}
Block Input/output Functions

• The block input and output functions are used to read and write data to binary files.

• The block read function is file read(fread).

• The block write function is file write(fwrite).

File Read (fread)

• fread reads a specified number of bytes from a binary file and places them into memory
at the specified location.

Declaration of fread ()

intfread ( void* pInArea,

int element Size,

int count,

FILE* sp);

• pInArea is a pointer to the input area in memory. A generic void pointer is used to allow
any pointer type to be passed to the function.

• elementSize and count are multiplied to determine how much data are to be transferred.

• The size is normally specified using the sizeof operator and the count is normally one
when reading structures.

• Operator and the count is normally one when reading structures.

• The last parameter is the associated stream.

• When fread is called, it transfers the next three integers from the file to the array, inArea.

• fread does not return end of file, it returns the number of elements read
File read (fread)

• Most common use of fread is reading structures(records).

• One advantage of block input/output functions is that one structure at a time can be
transferred.

• Second advantage is that the data need not be formatted.

Example: operation of fread when a structure is being read.

File Write (fwrite

• Writes a specified number of items to a binary file.

Declaration :

intfwrite(void* pOutArea,

intelementsize,
 int count,

FILE* sp);

File Write Operation

• Fwrite returns the number of items written.

• For example ,if it writes three integers, it returns 3. The return value, therefore, can be
use to test the write operation.

• If the number of items written is fewer than count, then an error has occurred. The
program should be aborted when we a write error is encountered.

Writing a Structure

Random Access file functions

Positioning Functions
• There are three file positioning functions:

1) Rewind the file (rewind)

2) Current location (ftell)

3) Set position (fseek)

1) Rewind File (rewind) Sets the file position indicator to the beginning of the file.

Declaration: void rewind(FILE* stream);

2) Current Location (ftell) Reports the current position of the file relative to the beginning
of the file.

• If the file position indicator is at the beginning of the file, ftell returns zero.

Declaration longintftell(FILE* stream);

• ftell returns the number of bytes from the beginning of the file.
• If these is a need to know the structure number relative to the first structure, then it must
be calculated by dividing the ftell return value by the size of the structure.

numchar =ftell(sp);

numstruct=numchar/sizeof(STRUCTURE_TYPE);

• Ftell returns – 1, if an error, is encountered.

Set Position (fseek): It positions the file location indicator to a specified byte position in a
file.

Decalonintfseek(FILE* stream, long offset, int wherefrom);

• Stream is a pointer to the open file.

• offset is a signed integer that specifies the number of bytes the position indicator must
move absolutely or relatively.

• C provides three named constants that can be used to specify the starting
point(wherefrom) of the seek.

#define SEEK_SET 0

#define SEEK_CUR 1

#define SEEK_END 2

• If wherefrom is SEEK_SET or 0 then the offset is measured absolutely from the

beginning of the file.

• To position the file marker to the next record in a structure file, execute the following
statement:

Fseek(sp,sizeof(STRUCTURE_TYPE),SEEK_CUR);

• If where from is SEEK_CUR or 1 then the displacement is calculated relatively from the
current file position

Syntax

fseek(sp, sizeof(STRUCTURE_TYPR), SEEK_CUR);

• If wherefrom is SEEK_END or 2, the file location indicator is positioned relative to the

end of file.

Syntax
fseek(stuFile, OL, SEEK_END);