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Positioning of file in C

Positioning() function in c

The fseek() function is utilized to change the document position of the stream . The fully extent of value from the source should be one of the constants SEEK_SET , SEEK_CUR , or SEEK_END , to show whether the offset is comparative  with the start of the record, the ongoing document position, or the finish of the document, individually.

seekg() function is utilized to reposition a document pointer in a record. The function takes the offset and relative situation from where we really want to move out pointer.

fseek() is utilized with its each of the 3 disagreement or specially involved in arguments alongside the other document functions to run out their particular purpose.

It is fundamentally a C function utilized for dealing with the document tasks. In C, document pointer is returned by the fopen() function(which is likewise an in-assembled function) utilized for opening any record in C and 'numbytes' is utilized to return the quantity of bytes from the document beginning.

By utilizing the fseek() capability in C, the ideal read and compose tasks can be performed by finding the document pointer and moving it appropriately.

The record position of a stream portrays where in the document the stream is right now perusing or composing.

I/O on the stream propels the record position through the document. on windows system the document position is addressed as a whole number, which counts the quantity of bytes from the very start of the record.

During I/O to a set of circumference circle record, you can change the document position at whatever point you wish, to peruse or compose any piece of the record. A few different sorts of documents may likewise allow this.

Documents which backing changing the record position are in some cases  to as irregular access documents.

For the following functions we use the positioning of files.

fseek() functions is the file handling functions in C programming language. It has following constants. SEEK_SET, SEEK_CUR, SEEK_END. Let’s see the total description and syntax for the above file handling functions.

Firstly lets see the fseek() function:

Fseek() :

he C library capability or function fseek() sets the record position of the stream to a given offset. The pointer related with the document is moved to that offset.

Syntax for the fseek() function:

Int fseek(FILE*stream, int offset, int whence);
  • Stream : points to the file object.
  • Offset: number of the bytes offset to the position.
  • Whence: the position where offset is added.

Whence defines that the point with respect to that where the file pointer needs to moved. It is specified by the following constants:

  • SEEK_END
  • SEEK_SET
  • SEEK_CUR

Lets see the following definitions:

  • SEEK_END: The seek_end function defines the end of the file pointer.
  • SEEK_SET: The seek_set function defines the beginning of the file pointer.
  • SEEK_CUR: The seek_cur function defines the current position of the file pointer

Lets see an example program for file positioning

#include <stdio.h>
int main()
{
FILE *fp;
fp = fopen("sample.txt", "r");
fseek(fp, 0, SEEK_END);
printf("Position of the file pointer is : ");
printf("%ld \n", ftell(fp));
fseek(fp,10,SEEK_SET);
int ch;
printf("the following result is: ");
while( (ch=fgetc(fp)) != EOF)
putchar(ch);
return 0;
}

Input:

Lets create a sample.text to store the input:
Lets create wonders

Output:

Position of the file pointer is : 9
The following result is: e wonders

In the above code, there is a document 'sample.txt' that as of now exists in the framework. To begin with, we are including the stdio.h library which is required to utilize fseek() function in C for any record related I/O activities.

 To start with, the record is opened utilizing the fopen() function and the document pointer is returned by it. Presently the fseek() function is utilized to move the record pointer to the furthest limit of the document.

After that the absolute number of document characters are imprinted on the control center or the place of the pointer which is at the remainder of the record is printed utilizing the 'ftell()' function.

fseek() function is again utilized to move the document pointer to the eleventh position and afterward the subsequent characters of record to attempt or ignore the initial 10 characters are imprinted on the center utilizing putchar() function.



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