Mastering the fseek Function in C Programming

fseek Function

The `fseek` function in C is used to set the file position indicator for a given file stream. It allows you to move the file pointer to a specific position within a file. Below is a detailed explanation of its functionality:

Declaration:

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

Parameters:

`stream`: A pointer to the `FILE` structure representing the file stream.
`offset`: The number of bytes to offset the file pointer from the specified origin. It can be positive, negative, or zero.
`origin`: A constant indicating the reference point for the offset. It can take one of the following values:
`SEEK_SET`: Beginning of the file.
`SEEK_CUR`: Current file position.
`SEEK_END`: End of the file.

Return Value:

Upon successful completion, `fseek` returns zero (`0`).
If an error occurs, or if the file positioning fails, `EOF` is returned.

Functionality:

1. File Positioning: `fseek` moves the file pointer associated with the stream `stream` to a new position within the file.
2. Offset Calculation: The `offset` parameter specifies the number of bytes to move the file pointer. It can be positive (forward), negative (backward), or zero (no movement).
3. Reference Point: The `origin` parameter determines the reference point for the offset. It specifies where the offset is applied from: - `SEEK_SET`: Beginning of the file. - `SEEK_CUR`: Current file position. - `SEEK_END`: End of the file.
4. Error Handling: `fseek` returns `EOF` if an error occurs during file positioning, such as seeking beyond the end of the file or attempting to seek on an unseekable stream.

Example:

#include <stdio.h>

int main() {
    FILE *file_ptr;
    long int position;

    // Open the file for reading
    file_ptr = fopen("example.txt", "r");

    // Move the file pointer to the 10th byte from the beginning of the file
    fseek(file_ptr, 10, SEEK_SET);

    // Get the current position of the file pointer
    position = ftell(file_ptr);
    printf("Current position: %ld\n", position);

    // Close the file
    fclose(file_ptr);

    return 0;
}

Notes:

`fseek` is commonly used to navigate within a file, especially when you need to read or write data at specific locations.
After positioning the file pointer using `fseek`, you can perform read or write operations starting from that position.
It's important to handle error cases, such as when `fseek` returns `EOF`, to ensure proper error detection and handling in your program.
Remember to open the file in an appropriate mode (`"r"`, `"w"`, `"a"`, etc.) before using `fseek`.

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fseek Function in C Programming

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