Iseek() function in C

Iseek() function in C


Introduction to lseek() Function in C

In C programming, lseek() is a crucial function for handling file input/output operations, allowing precise positioning within files.

Understanding its usage is essential for efficient file manipulation and data access.

 The lseek() function repositions the file offset of an open file descriptor, enabling seeking to a specific position within the file.

It supports both forward and backward seeking, facilitating random access to files.

Syntax lseek() Function in C:

#include <stdio.h>
off_t lseek(int fd, off_t offset, int whence);

Example Program:

// Program for Lseek() Function in C
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>

int main() {
    int fd;
    off_t position;

    fd = open("example.txt", O_RDONLY); // Open file in read-only mode

    if (fd != -1) {
        position = lseek(fd, 0, SEEK_END); // Seek to the end of file
        printf("File size: %ld bytes\n", (long)position);
        close(fd); // Close file
    } else {
        printf("Error opening file.\n");

    return 0;


File size:  bytes

Uses and Application Complexity

 Random Access: lseek() allows applications to access files randomly by positioning the file pointer.

 File Truncation: It can be used to truncate files by setting the file size to a specified offset.

 Sequential Access: While primarily used for random access, lseek() can also facilitate sequential file processing by repositioning the file pointer.

Application Complexity

 Low Complexity: Basic usage of lseek() for simple file operations such as determining file size or positioning the file pointer has low complexity.

 Moderate Complexity: More complex applications involving frequent seeking or concurrent file access may require careful synchronization and error handling.

 High Complexity: Advanced applications, such as database management systems or file systems, may involve intricate logic for efficient file manipulation using lseek().

 Understanding the nuances of lseek() is crucial for efficient file handling in C programming, enabling precise data access and manipulation within files of various sizes and formats.

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