This document discusses file input/output (I/O) operations in C programming. It covers opening, closing, reading from and writing to files. Specific file I/O functions covered include fopen(), fclose(), getc(), putc(), getw(), putw(), fprintf(), fscanf(), feof(), ferror(), fseek(), ftell(), and rewind(). Error handling during file I/O and random access to files using functions like fseek() are also discussed. Examples are provided to demonstrate reading integer and mixed data types from files and writing data to files.

1. Pointers
Topics
 File and it’s operation
 Opening and Closing file
 Input/Output Operations on Files

2. File and It’s Operation
 File: A file is a place on the disk where a
group of related data is stored.
 File Operations:
1. Naming a file
2. Opening a file
3. Reading data from a file
4. Writing data to a file
5. Closing a file

3. Opening and Closing a file
 Opening a File: The general format for declaring
and opening a file:
FILE *fp;
fp = fopen(“filename”,”mode”);
Here filename is a valid name and mode can be
one of the following:
r – open the file for reading only
w – open the file for writing only
a - open the file for appending data to it
 Closing a file: The general form:
fclose(file_pointer);

4. Input/Output Operations on Files
 putc(): It writes a character to the file
specified by the file pointer. The general
format is-
putc(c,fp);
 getc(): It reads a character from a file
specified by the file pointer. The general
format is-
c=getc(fp);

5. Writing to and Reading from a File
main()
{
FILE *fp;
char c;
fp=fopen(“Sample”,”w”);
while((c=getchar())!=‘n’)
putc(c,fp);
fclose(fp);
fp=fopen(“Sample”,”r”);
While((c=getc(fp)!=EOF)
printf(“%c”,c);
getch();
}

6. Input/Output Operations on Files
 putw(): It writes an integer to a file specified
by the file pointer. The general format is-
putw(integer, fp);
 getw(): It reads an integer from a file
specified by the file pointer. The general
format is-
n=getw(fp);

7. Input/Output Operations on Files
 fprintf(): It writes a group of mixed data
items to the file specified by the file pointer.
The general format is-
fprintf(fp,”control string”,list);
 fscanf(): It reads a group of mixed data
items from a file specified by the file pointer.
The general format is-
fscanf(fp,”control string”,list);

8. Handling of Integer data files
main()
{
FILE *fp;
int x,k;
fp=fopen(“Sample”,”w”);
for(k=1;k<=10;k++)
{ scanf(“%d”,&x);
putw(x,fp);}
fclose(fp);
fp=fopen(“Sample”,”r”);
for(k=1;k<=10;k++)
{ x=getw(fp);
printf(“%d ”,x}
fclose(fp);
}

9. Handling of files with mixed data types
main()
{
FILE *fp;
int x,k;
float y;
fp=fopen(“Sample”,”w”);
for(k=1;k<=10;k++)
{ scanf(“%d %f”,&x,&y);
fprintf(fp,”%d %f”,x,y); }
fclose(fp);
fp=fopen(“Sample”,”r”);
for(k=1;k<=10;k++)
{ fscanf(fp,”%d %f”,&x,&y);
printf(“n%d %f ”,x,y}
fclose(fp);
}

10. Error Handling during I/O Operation
 Reasons of error during file operation:
1. Trying to read beyond the end-of-file
mark.
2. Device overflow
3. Trying to use a file that has not been
opened.
4. Trying to perform an operation on a file,
when the file is opened for another type of
operation
5. Opening a file with an invalid filename
6. Attempting to write to a write-protected

11. Continue…
 The feof() function can be used to test for an end of the file
condition. If fp is a pointer to file that has just been opened
for reading, then the statement
if(feof(fp))
printf(“End of the file”);
would display the message “End of the file” on reaching the
end of file condition.
 The ferror() function reports the status of the file indicated.
It returns nonzero integer if an error has been detected
upto that point otherwise returns zero. The statement
if(ferror(fp) !=0)
printf(“An error has occurred”);
would print the error message if the reading is not
successful.

12. Random Access to Files
 When we are interested in accessing only a
particular part of a file and not in reading the
other parts, then we need some other
functions named fseek, ftell and rewind.
 Ftell() takes a file pointer and returns a
number of type long, that corresponding to
the current position. The form-
n = ftell(fp);
n would give the relative offset (in bytes) of
the current position.

13. Continue…
 rewind() takes a file pointer and reset the position
to the start of the file.
rewind(fp);
 Fseek() is used to move the file position to a
desired location within the file. The general format
is
fseek(file_pointer, offset, position);
file_pointer is a pointer to the file concerned, offset
is a number or variable of type long and position is
an integer number. The offset specifies the
number of positions (bytes) to be moved from the
location specified by position.

14. Continue…
 Example of fseek():
fseek(fp,0L,0); go to the beginning
fseek(fp,0L,1); stay at current position
fseek(fp,0L,2); go to the end of the file
fseek(fp,m,0); move to (m+1)th byte in the file
fseek(fp,m,1); go forward by m bytes
fseek(fp,-m,1); go backward by m bytes from
current position
fseek(fp,-m,2); to backward by bytes from the end

15. Use of fseek and ftell function
main()
{
FILE *fp;
long n;
char c;
fp = fopen(“Random”,”w”);
while((c=getchar())!=‘n’)
putc(c,fp);
printf(“Number of char = %dn”,ftell(fp));
fclose(fp);
fp = fopen(“Random”,”r”);
n = 0L;

16. Continue…
while(feof(fp) = = 0)
{
fseek(fp, n, 0);
printf(“position of %c is %ldn”,getc(fp),ftell(fp);
n = n+5L;
}
putchar(“n”);
fseek(fp,-1L,2);
do{
putchar(getc(fp));
}while(!fseek(fp,-2L,1));
fclose(fp);
}