Which Function is used to Reposition the File Pointer

Last Updated on November 27, 2023 by Ankit Kochar

In the realm of file handling in programming, manipulating file pointers is fundamental for efficient data retrieval and manipulation. The file pointer serves as a critical marker within a file, indicating the current position during read or write operations. One of the essential functionalities in file handling is the ability to move this pointer to different locations within the file. This article aims to delve into the function responsible for repositioning the file pointer, exploring its significance and usage in various programming languages.

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
Effectively managing file pointers is indispensable in file handling operations in programming. The ability to reposition the file pointer using functions like fseek() empowers programmers to navigate through files seamlessly, enabling efficient data manipulation and extraction. Understanding and utilizing these functions not only facilitate better file handling but also enhance the overall efficiency and functionality of programs dealing with file operations.

Frequently Asked Questions(FAQS) Related to function used to Reposition The File Pointer:

Here are some FAQs related to Function used to Reposition the File Pointer.

Q1: What is the file pointer in programming?
The file pointer is a marker or indicator that denotes the current position within a file during read or write operations. It keeps track of the location within the file where the next operation will occur.

Q2: Why is repositioning the file pointer important?
Repositioning the file pointer is crucial for accessing specific parts of a file during reading or writing. It allows programmers to move to desired locations within the file to perform operations such as appending, overwriting, or reading specific data.

Q3: Which function is used to reposition the file pointer?
In various programming languages like C, C++, and Python, functions like fseek(), fseeko(), or seek() are commonly used to reposition the file pointer. These functions enable programmers to move the file pointer to a specified location within the file.

Q4: How does fseek() function work?
The fseek() function in C and C++ allows the file pointer to be moved to a specific location within the file. It takes three arguments: the file pointer, the offset (number of bytes to move), and the reference position (beginning, current, or end of the file).