File handling in c

 File is a sequence of bits, bytes, lines or records whose meaning is defined by its
creator and user i.e. file is a collection of related data that a computers treats as a
single unit.
 When a computer reads a file, it copies the file from the storage device to memory;
when it writes to a file, it transfers data from memory to the storage device.
 FILE HANDLING in C programming uses FILE STREAM as a means of
communication between programs and data files.
 The INPUT STREAM extracts the data from the files and supplies it to the
program
 The OUTPUT STREAM stores the data into the file supplied by the program

The header file used for file handling is
<FSTREAM.H>
includes
IFSTREAM OFSTREAM
TO HANDLETHE INPUT FILES
It supports all the input operations
such as :
open(), get(), getline(),read(),
seekg(), tellg()
TO HANDLETHE OUTPUT FILES
It supports all the output operations
such as :
open(), put(), write(), seekp(), tellp()

Data files
 Can be created, updated, and processed by C programs
 Storage of data in variables and arrays is only temporary
Data files are of two types
TEXT FILES BINARY FILES
Saves the data in the form of ASCII
codes
It consist of sequential characters
divided into lines. Each line terminates
with the newline character (n).
Saves the data in Binary codes
It consist of data values such as
integers, floats or complex data types,
“using their memory representation.”

 Opening a file
 Reading data from a file
 Writing data to a file
 Closing a file

 ios::in open for reading
 ios::out open for writing
 ios::app writing contents at the eof
 ios::binary open as binary file
 ios::noreplace open fails if file already exist
 ios::nocreate open fails if file doesn’t exist
 ios::ate go to the eof at opening time
 ios::trunc truncate the file if it already exists

1. Create the stream via a pointer variable using
the FILE structure:
FILE *fp;
2. Open the file, associating the stream name
with the file name.
3. Read or write the data.
4. Close the file.

A file must be “opened” before it can be used.
FILE *fp;
fp = fopen (filename, mode);
fp = fopen (“myfile.dat”, “w”);
 fp is declared as a pointer to the data type FILE.
 filename is a string - specifies the name of the file.
 fopen returns a pointer to the file which is used in all
subsequent file operations.

 When you open a file you must also specify what
you wish to do with it i.e. Read from the file, Write
to the file, or both.
 You may use a number of different files in your
program. you must specify when reading or writing
which file you wish to use.This is accomplished by
using a variable called a file pointer.
 Every file you open has its own file pointer
variable. When you wish to write to a file you
specify the file by using its file pointer variable.

 You declare these file pointer variables as follows:
FILE *fp1, *fp2, *fp3;
 The variables fp1, fp2, fp3 are file pointers.You may use
any name you wish.
 A file pointer is simply a variable like an integer or
character. It does not point to a file or the data in a file. It is
simply used to indicate which file your I/O operation
refers to.

MODE is a string which specifies the purpose of opening the
file

 Read+ (r+) : It is an extension to the read mode. It opens a file for update.
Operations possible using this mode are reading the contents of an existing file,
writing new contents, modifying the existing ones. Returns NULL if file doesn’t
exist.
 Write+ (r+) : Similar to the write mode. It creates a file for update.
Operations that can be performed are write new contents and read and modify
the back
 Append+ (r+) :It opens or creates a file for update. Similar to append mode
and operations to be performed are read existing file, add new contents at the
end of the file. Cannot modify existing contents

 When we finish with a mode, we need to close the file before
ending the program or beginning another mode with that same file.
 Syntax : fclose (filepointer) ;
FILE *xyz ;
xyz = fopen (“test”, “w”) ;
…….
fclose (xyz) ;

#include<stdio.h>
#include<conio.h>
main()
{
FILE * fp;
fp=fopen(“abc.c”,”r”);
if(fp==NULL)
{ printf(“file cannot open”);
exit(1);
}
fclose(fp);
getch();
}

Functions for reading a character from a file are
 fgetc()
 getc()
syntax: ch = fgetc (fp) ;
ch = getc (fp) ;
It returns a character read from the file to which “fp” points to and
stores this value in the variable file to “ch”. The fp pointer then
automatically points to the next character in the file (char is of 1
byte)
THIS IS MY FIRST FILE

getw();
This functions is an integer oriented function.This is used for reading a
integer character from a file in which numbers are stored
syntax:: a = getw (fp) ;
The numbers read will be stored in the integer type variable “a”
and “fp” file pointer automatically moves forward by 2 bytes file
pointer (int is of 2 bytes). It uses binary mode.

fscanf();
Reads any type of variable i.e char, int, float, string etc. from the
file. It behaves similar to the console input function scanf , the only
difference it works with files.
syntax: fscanf ( fp , “ %c ” , &ch) ;
file pointer control string char type variable
If in case of “fp” we put “stdin” it would work similar to scanf();

fgets(); or gets();
This function is used to read strings from the file
syntax: fgets (str , n , fp) ;
It returns a string read upto n characters or upto the end of the
string i.e null character ‘0’.When all the lines from the file are read
and we attempt to read one more line, fgets() returns a null value.

Functions for writing a character or number in a file are
 fputc()
 putc()
syntax: putc ( ch , fp );
fputc ( ch , fp );
Both these functions write a character in the file at the position
specified by the pointer.The value of a variable ch is written in the
file by fp.
The fp pointer then automatically moves to the end of the
character after printing characters in the file, that next character
could be written on next position. It uses the file in the text mode.

putw();
This functions is an integer oriented function.This is used for
printing an integer character in a file.
syntax:: putw ( a , fp ) ;
The integer value of a is written in file by fp and then “fp” file
pointer automatically moves forward by 2 bytes file pointer (int is
of 2 bytes) and prints the next character. It uses binary mode.

fprintf();
Prints any type of variable i.e. char, int, float, string etc. in the file. It
behaves similar to the console input function printf , the only
difference it works with files.
syntax: fprintf ( fp , “ %d ” , ch) ;
file pointer control string char type variable
If in case of “fp” we put “stdout” it would work similar to printf();

fputs(); or puts();
This function is used to write strings in the file
syntax: fputs (str , fp) ;
fwrite();
It transfers a specified number of bytes beginning at a specified location in
memory to termed as a structure to a file.The data is written beginning at the
location in the file indicated by the file position pointer.
syntax:
fwrite( structure , size-of-structure , starting value , file pointer)
fwrite( &e , sizeof (e) , 1 , fp)

How to check EOF condition when using fscanf?
Use the function eof
if (eof (fp))
printf (“n Reached end of file”) ;
How to check successful open?
For opening in “r” mode, the file must exist.
if (fp == NULL)
printf (“n Unable to open file”) ;

While reading from a data file, if we want to read the
complete file i.e. till the end of data , then an end of file
marker should be checked.
 EOF :: EOF is a character and every character read from the file is
compared against this character.
while ( a = getc(fp) != eof )
putc ( a, f1 );
 feof(); :: feof() is a macro which returns 0 if end of file is not
reached. If end of file is reached it returns a non zero value.
if ( feof ( fp ) )
printf( “ the end of file is reached”);

void main()
{ FILE *fopen(), *fp;
int c ;
char filename[40] ;
printf(“Enter file to be displayed: “);
gets( filename ) ; // take in the filename as a string
fp = fopen( filename, “r”); // opens the file in read mode
c = getc( fp ) ; // reads the first character of the file
while ( c != EOF )
{ putc(c); //displays the character as it reads
c = getc ( fp );
}
fclose( fp );
}

NOTE: If the file is empty, we are at the end, so getc returns EOF
a special value to indicate that the end of file has been
reached. (Normally -1 is used for EOF)
Alternatively, you could prompt the user to enter the filename again, and try to
open it again:
fp = fopen (fname, “r”) ;
while ( fp == NULL)
{
printf(“Cannot open %s for reading n”, fname );
printf(“nnEnter filename :” );
gets( fname );
fp = fopen (fname, “r”) ;
}

 Read/Write functions in standard library
 fgetc
▪ Reads one character from a file
▪ Takes a FILE pointer as an argument
▪ fgetc( stdin ) equivalent to getchar()
 fputc
▪ Writes one character to a file
▪ Takes a FILE pointer and a character to write as an argument
▪ fputc( 'a', stdout ) equivalent to putchar( 'a' )
 fgets
▪ Reads a line from a file
 fputs
▪ Writes a line to a file
 fscanf / fprintf
▪ File processing equivalents of scanf and printf

32
main() {
FILE *in, *out ;
char c ;
in = fopen (“infile.dat”, “r”) ;
out = fopen (“outfile.dat”, “w”) ;
while ((c = getc (in)) != EOF)
putc (toupper (c), out);
fclose (in) ;
fclose (out) ;
}

Fputc();
If we want we can also print the contents from the file and directly
on the printer using fputc()
syntax: fputc (ch , stdprn) ;
Where stdprn is the standard file pointer used instead of user
defined file pointer. It means that the data should be written on the
printer and not on the file.

File handling in c

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File handling in c