C
  • Introduction
    • Fundamentals of a Program
    • Overview of C
    • Features of C
  • Installing Required Software
    • Setting Up VSCode for Windows
    • Setting Up VSCode for macOS
    • Setting Up VSCode for Ubuntu
  • Starting to write code
    • Compiling and Running Your Code
    • Creating Our First C Program
    • Errors and Warnings
    • Program: Writing a C Program to Display Your Name
    • Structure of a C Program
  • Basic Concepts
    • Comments in C
    • Preprocessor in C
    • The #include Statement
    • Displaying Output
    • Reading Input from the Terminal
    • Enums and Chars
    • Data Types and Variables
    • Format Specifiers
    • Command Line Arguments
    • Program: Calculating the Area of a Triangle
  • Operators
    • Converting Minutes to Years and Days
    • Basic Operators
    • Bitwise Operators
    • Program: Byte Sizes of Basic Data Types
    • cast and sizeof Operators
    • Operator Precedence
  • Control Flow
    • If-Else Statements
    • Program: Weekly Pay Calculation
    • Switch Statement
    • For Loop
    • While and Do-While Loops
    • Nested Loops and Loop Control
    • Program: Guess the Number
  • Arrays
    • Introduction to Arrays
    • Program: Prime Number Generator
    • Multidimensional Arrays
    • Program: simple Weather Program
    • Variable Length Arrays (VLAs)
  • Functions
    • Overview of Functions
    • Defining Functions
    • Arguments and Parameters
    • Returning Data from Functions
    • Variable Scoping
    • Program: Tic Tac Toe Game
    • Recursion
  • Strings
    • Defining a String
    • Constant Strings in C
    • Common String Functions
    • Program: Bubble Sort
    • Searching, Tokenizing, and Analyzing Strings
    • Converting Strings
  • Debugging
    • What is Debugging
    • Understanding the Call Stack
    • Common C Mistakes
    • Understanding Compiler Errors
  • Pointer
    • Defining Pointers
    • Accessing Pointers
    • Program: Pointer Demonstration
    • Pointers and Const
    • Void Pointers
    • String Pointers
    • Array Pointers
    • Utilizing Pointers with Functions
    • Pointer Arithmetic
  • Dynamic Memory Allocation
    • malloc, calloc, and realloc
    • Program: User Input String
    • Memory Deallocation
  • Structure
    • Structures and Arrays
    • Nested Structures
    • Structures and Pointers
    • Structures and Functions
    • Program: Structure pointers and Functions
  • File Input and Output
    • Accessing Files
    • Reading from a File
    • Program: Finding the Total Number of Lines in a Text File
    • Writing to a Text File
    • Finding Your Position in a File
    • Program: Converting Characters in a File to Uppercase
    • Program: Printing the Contents of a File in Reverse Order
  • The Standard C Library
    • Various Functions in C
    • Math Functions in C
    • Utility Functions in C
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On this page
  • Overview
  • 1. File Position Indicator
  • 2. Moving the Position Indicator
  • 3. Repositioning to the Beginning
  • 4. Repositioning to the End
  • 5. Repositioning Relative to Current Position
  • 6. Returning to the Original Position
  • 7. Example: Reading a Specific Section of a File

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  1. File Input and Output

Finding Your Position in a File

Overview

Determining your position in a file in C involves using functions to move the file position indicator. This page provides an overview of the functions and techniques for finding and manipulating the position within a file.

1. File Position Indicator

  • Every file has a position indicator that keeps track of the current position within the file.

    long currentPosition = ftell(filePointer);

  • Use the ftell function to get the current position in bytes. This function returns a long value.

2. Moving the Position Indicator

  • Use the fseek function to move the position indicator to a specified location.

    fseek(filePointer, offset, SEEK_SET);

  • The second parameter, offset, determines the number of bytes to move. The third parameter specifies the starting point (SEEK_SET for the beginning of the file, SEEK_CUR for the current position, and SEEK_END for the end of the file).

3. Repositioning to the Beginning

  • Move the position indicator to the beginning of the file.

    fseek(filePointer, 0, SEEK_SET);

4. Repositioning to the End

  • Move the position indicator to the end of the file.

    fseek(filePointer, 0, SEEK_END);

  • This can be useful for appending data to the end of a file.

5. Repositioning Relative to Current Position

  • Move the position indicator a certain number of bytes forward or backward from the current position.

    fseek(filePointer, -100, SEEK_CUR); // Move 100 bytes backward

6. Returning to the Original Position

  • Store the current position and later return to it using fseek.

    long originalPosition = ftell(filePointer);
// Perform some operations
fseek(filePointer, originalPosition, SEEK_SET); // Return to the original position

7. Example: Reading a Specific Section of a File

  • Use fseek to move to a specific position and read a portion of the file.

    fseek(filePointer, 50, SEEK_SET); // Move to byte 50
char buffer[10];
fread(buffer, sizeof(char), 10, filePointer); // Read 10 characters from this position

Understanding and manipulating the file position indicator is crucial for reading, writing, and modifying specific portions of a file. These functions provide flexibility in navigating and managing file content efficiently.

If you have specific questions or if there are additional topics you'd like to explore, feel free to ask!

PreviousWriting to a Text FileNextProgram: Converting Characters in a File to Uppercase

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