See the lseek_example. c file. Modify the lseek_example. c, such that it reads from an input file (named "start. txt") and will print to an output file (named "end. txt") every (1+3*i)th character, starting from the 1st character in the input file. In other words, it will print the 1st character, then skip 2 characters and print the 4th one, then skip 2 characters and print the 7th one, and so on. For instance, for input file:
ABCDEFGHIJKLM
It will output:
ADGJM
Iseek_example. c file contant:
// C program to read nth byte of a file and
// copy it to another file using lseek
#include
#include
#include
#include
void func(char arr[], int n)
{
// Open the file for READ only.
int f_read = open("start. txt", O_RDONLY);
// Open the file for WRITE and READ only.
int f_write = open("end. txt", O_WRONLY);
int count = 0;
while (read(f_read, arr, 1))
{
// to write the 1st byte of the input file in
// the output file
if (count < n)
{
// SEEK_CUR specifies that
// the offset provided is relative to the
// current file position
lseek (f_read, n, SEEK_CUR);
write (f_write, arr, 1);
count = n;
}
// After the nth byte (now taking the alternate
// nth byte)
else
{
count = (2*n);
lseek(f_read, count, SEEK_CUR);
write(f_write, arr, 1);
}
}
close(f_write);
close(f_read);
}
// Driver code
int main()
{
char arr[100];
int n;
n = 5;
// Calling for the function
func(arr, n);
return 0;
}

See the lseek_example.c file. Modify the lseek_example.c, such that it reads from an input file (named "start.txt") and will print to an output file (named "end.txt") every (1+3*i)th character, starting from the 1st character in the input file. In other words, it will print the 1st character, then skip 2 characters and print the 4th one, then skip 2 characters and print the 7th one, and so on.

For instance, for input file:

ABCDEFGHIJKLM

It will output:

ADGJM

Iseek_example.c file contant:

// C program to read nth byte of a file and

// copy it to another file using lseek

#include

#include

#include

#include

void func(char arr[], int n)

{

// Open the file for READ only.

int f_read = open("start.txt", O_RDONLY);

// Open the file for WRITE and READ only.

int f_write = open("end.txt", O_WRONLY);

int count = 0;

while (read(f_read, arr, 1))

{

// to write the 1st byte of the input file in

// the output file

if (count < n)

{

// SEEK_CUR specifies that

// the offset provided is relative to the

// current file position

lseek (f_read, n, SEEK_CUR);

write (f_write, arr, 1);

count = n;

}

// After the nth byte (now taking the alternate

// nth byte)

else

{

count = (2*n);

lseek(f_read, count, SEEK_CUR);

write(f_write, arr, 1);

}

}

close(f_write);

close(f_read);

}

// Driver code

int main()

{

char arr[100];

int n;

n = 5;

// Calling for the function

func(arr, n);

return 0;

}

Explanation:

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credit to ace:  

batradivjyot25.  

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