Which Function is used to Reposition the File Pointer

The C programming language provides us with a number of functions to help us with this task. fseek is one of these functions (). The function fseek() is a C standard library function found in the stdio.h header file. It is used to move or change the offset position of the file pointer that is being used to read the file.

What is a File Pointer?

A file pointer is a special pointer pointing to a structure known as the "file stream," which represents a file opened for reading, writing, or both. The file pointer performs various operations on the file, such as reading from or writing to it, moving the current position within the file, and closing the file.

The syntax for file pointer in C:

FILE *fp;

Explanation of syntax for file pointer in C:
You can create a file pointer by declaring a variable of type FILE* defined in header file stdio.h.

Example for file pointer:

#include <stdio.h>
int main(){
    FILE *fp;
    fp = fopen("file.txt", "r");
    return 0;
}

Explanation of file pointer:
To open a file, you can use the ‘fopen()’ function, and the mode in which we want to open as "r" for a read. The ‘fopen()’ function returns a pointer to the file stream, which you can assign to the file pointer variable.

Function used to Reposition the File Pointer

The function used to reposition the file pointer depends on the programming language and the specific library being used to interact with files. In the C programming language, the fseek() function is used to reposition the file pointer. It takes three arguments: the file pointer to be moved, the offset (number of bytes) to move the pointer by, and the origin point from which to move the pointer.

fseek():

The file pointer is set to the provided offset using the fseek() method. With it, data can be written into a file at a specific location.

Syntax for fseek():

int fseek(FILE *stream, long int offset, int origin)  

Explanation of syntax for fseek():
In the syntax for fseek(), stream is a pointer to the file stream to modify. offset is the file position indicator. origin specifies the starting point for the offset.

Example of fseek() in C:

#include <stdio.h>

int main () {
   FILE *fp;

   fp = fopen("file.txt","w+");
   fputs("welcome",fp);
  
   fseek( fp, 7, SEEK_SET );
   fputs(" this is fseek", fp);
   fclose(fp);
   
   return(0);
}

Output

file.txt
welcome this is fseek

Explanation of fseek():
In fseek() example program, we have created a file pointer named as FILE* and then we created a file.txt. To open a file we use fopen() and write mode operation to write some text in it. Now we took fseek() function to join the text which we have written using the file pointer and finally we closed the function using fclose(). We get the result as “welcome this is fseek”

Conclusion
In conclusion, repositioning the file pointer is an important operation when working with files in a computer program. By changing the current position of the file pointer, you can read or write data from a specific location within the file. The file pointer can be repositioned using various functions and methods depending on the programming language or environment being used, such as fseek() in C or seek() in Python. It is important to use these functions with caution and to ensure that the file is open and accessible before attempting to reposition the file pointer. Overall, understanding how to reposition the file pointer is a fundamental skill for anyone working with files in computer programming.

Frequently Asked Questions(FAQS):

1. What is fseek() in c?
When we are working with different files in our code, the C language provides us with a wide range of distinct functions to help us with this task. fseek is one of these functions (). The function fseek() is a C standard library function found in the stdio.h header file. It is used to move or change the offset position of the file pointer that is being used to read the file.

2. What is file repositioning?
Rearranging items within a file. The current-file-position pointer is re – positioned to a given value after the file is searched for the appropriate entry. Reposition within a file does not require any I/O. This is also referred to as a file seek. A file is being deleted.

3. What is the fseek return value?
Value returned. If the fseek() or fseeko() function successfully moves the pointer, it returns 0. An error is indicated by a nonzero return value. The return value is nonzero on devices that cannot seek, such as terminals and printers.

4. What is the purpose of the fseek function?
The fseek() function searches a file that is currently open. This function begins to move the file pointer from the current position to the a new position indicated by the amount of bytes, either forward or backward.

5. What are the C fseek commands?
Example of fseek() in C/C++:fseek() is a function that moves the file pointer associated with a particular file to a specific position. position specifies the point to which the file pointer must be moved.