QUES 21 FILE COPY PROGRAM

C LANGUAGE BOOK

 The FILE structure has been defined in the header file “stdio.h”
 FILE  *fp ;
fopen( ) returns the address of this structure, which we have
collected in the structure pointer called fp.

File Opening Modes

In our first program on disk I/O we have opened the file in read
(“r”) mode. However, “r” is but one of the several modes in which
we can open a file. Following is a list of all possible modes in
which a file can be opened. The tasks performed by fopen( ) when
a file is opened in each of these modes are also mentioned.

"r"  Searches file. If the file is opened successfully  fopen( )
loads it into memory and sets up a pointer which points to
the first character in it. If the file cannot be opened fopen( )
returns NULL.
Operations possible – reading from the file.

"w"  Searches file. If the file exists, its contents are overwritten.
If the file doesn’t exist, a new file is created. Returns
NULL, if unable to open file.
Operations possible – writing to the file.

"a"  Searches file. If the file is opened successfully  fopen( )
loads it into memory and sets up a pointer that points to the
last character in it. If the file doesn’t exist, a new file is
created. Returns NULL, if unable to open file.
Operations possible - adding new contents at the end of file.

 "r+"  Searches file. If is opened successfully fopen( ) loads it into
memory and sets up a pointer which points to the first
character in it. Returns NULL, if unable to open the file. 
 Operations possible - reading existing contents, writing new
contents, modifying existing contents of the file.

"w+"  Searches file. If the file exists, its contents are overwritten.
If the file doesn’t exist a new file is created. Returns NULL,
if unable to open file.
Operations possible - writing new contents, reading them
back and modifying existing contents of the file.

"a+"  Searches file. If the file is opened successfully  fopen( )
loads it into memory and sets up a pointer which points to
the first character in it. If the file doesn’t exist, a new file is
created. Returns NULL, if unable to open file.
Operations possible - reading existing contents, appending
new contents to end of file. Cannot modify existing
contents.

rb:-open a binary file for reading.
wb:-create a binary file for writing.
ab:-append to a binary file
r+b:-open a binary file for read/write.
w+b:-create a binary file for read/write.
a+b:-append or create  a binary file for read/write.


fs = fopen ( argv[1], "r" ) ;
it open file in reading mode.r denotes mode.


ft = fopen ( argv[2], "w" ) ;
it open file in writing mode.w denotes mode.

 EOF denotes end of file.The EOF macro has been defined in the
file “stdio.h”.
fgetc( ) which reads characters from a file. The file signified by file pointer.
fputc( ) which writes characters to a file. The file signified by file pointer.

Reading from a File 
To read the file’s contents from memory there exists a function
called fgetc( ). This has been used in our program as,

ch = fgetc ( fp ) ;


Writing to a File 
To write the content to a file. there exists a function
called fputc( ). fputc ( ch, ft ) ;
 ch is character.ft is file pointer in our program.

writes strings to a file
writes strings to a file using the function fputs( ).
fputs ( s, ft ) ;
s is string.ft is file pointer.

fputs( ) function then writes the contents of the array to the disk. Since
fputs( ) does not automatically add a newline character to the end
of the string, we must do this explicitly to make it easier to read
the string back from the file.
fputs ( "\n", ft ) ;


Closing the File
When we have finished reading from the file, we need to close it.
This is done using the function fclose( ) through the statement,

fclose ( fp ) ;


if you save program as filecopy.c.then

To compile the program type at command
prompt, in the form:

filecopy  PR1.C  PR2.C 

where, PR1.C is the source filename and PR2.C is the target
filename.


/*
WAP TO COPY ONE FILE TO ANOTHER.
*/


#include "stdio.h" 
main ( int  argc, char *argv[ ] )
{
 FILE  *fs, *ft ;
 char  ch ;

 if ( argc != 3 )
 {
  puts ( "Improper number of arguments" ) ;
  exit( ) ;
 }

 fs = fopen ( argv[1], "r" ) ;
 if ( fs == NULL )
{
  puts ( "Cannot open source file" ) ;
  exit( ) ;
 }

 ft = fopen ( argv[2], "w" ) ;
 if ( ft == NULL )
 {
  puts ( "Cannot open target file" ) ;
  fclose ( fs ) ;
  exit( ) ;
 }

 while ( 1 )
 {
  ch = fgetc ( fs ) ;

  if ( ch == EOF )
   break ;
  else
   fputc ( ch, ft ) ;
 }

fclose ( fs ) ;
fclose ( ft ) ;
}


fscanf( )
fscanf( )  library functions to read data from file.
  fscanf ( fp, "%s %d %f", e.name, &e.age, &e.bs )
fp is file pointer.

fprintf( ):-
fprintf( ), which writes the values in the structure variable to the file.
This function is similar to  printf( ), except that a  FILE pointer is
included as the first argument.
fprintf ( fp,"\n%s %d %f", e.name, e.age, e.bs ) ;
 fp is file pointer.

fflush( ).:-
  It is designed to remove or ‘flush out’ any data remaining in the buffer.
The argument to  fflush( ) must be the buffer which we want to flush out.
Here we have used ‘stdin’, which means buffer related with standard input
device—keyboard. 

/* Read records from a file using structure */
#include "stdio.h"
main( )
{
 FILE  *fp ;
 struct emp 
 {
  char  name[40] ;
  int  age ;
  float  bs ;
 } ;
 struct emp  e ;

 fp = fopen ( "EMPLOYEE.DAT", "r" ) ;

 if ( fp == NULL )
 {
  puts ( "Cannot open file" ) ;
  exit( ) ;
 }

 while ( fscanf ( fp, "%s %d %f", e.name, &e.age, &e.bs ) != EOF )
  printf ( "\n%s %d %f", e.name, e.age, e.bs ) ; 

 fclose ( fp ) ;
}

And here is the output of the program...

x 34 1250.500000
xx 21 1300.500000
xxx 34 1400.500000

C LANGUAGE BOOK