File Error Handling

File Error Handling in C: The Guardian of Your Data 🛡️

The Story of the Careful Librarian

Imagine you’re a librarian managing a huge library. Every day, people come to borrow and return books. But what happens when:

• Someone asks for a book that doesn’t exist?
• The library closes while you’re still reading?
• Someone tries to rename a book that’s already borrowed?

File Error Handling in C is like being this careful librarian—always checking if things went wrong and knowing exactly what to do when they do!

🎯 What We’ll Learn

graph TD
    A["File Error Handling"] --> B["EOF Handling"]
    A --> C["ferror & feof"]
    A --> D["remove & rename"]
    B --> E["Detecting End of File"]
    C --> F["Checking What Went Wrong"]
    D --> G["Deleting & Renaming Files"]

📚 Part 1: EOF Handling — “The End of the Book”

What is EOF?

EOF stands for End Of File.

Think of it like reaching the last page of a book. You’ve read everything—there’s nothing more to read!

Simple Example:

• You’re reading a storybook page by page
• When you flip past the last page… that’s EOF!
• The book says “The End” and you know to stop

How EOF Works in C

When you read from a file, C needs to tell you when there’s nothing left. It uses a special signal called EOF (which is usually the number -1).

#include <stdio.h>

int main() {
    FILE *book = fopen("story.txt", "r");
    int ch;

    // Read character by character
    while ((ch = fgetc(book)) != EOF) {
        printf("%c", ch);
    }
    // We've reached the end!
    printf("\n--- The End ---\n");

    fclose(book);
    return 0;
}

🔑 Key Points About EOF

Real Life Example

// Reading numbers until file ends
int number;
while (fscanf(file, "%d", &number) != EOF) {
    printf("Found: %d\n", number);
}

🔍 Part 2: ferror and feof — “The Detective Tools”

The Problem

Here’s a puzzle: When reading stops, was it because:

1. We reached the end of the file? (Good!)
2. Something went wrong? (Bad!)

Both cases might look the same! That’s why C gives us two detective tools.

Meet feof() — “Did we finish reading?”

feof() checks if we’ve reached the end of the file.

if (feof(file)) {
    printf("Reached the end! All done.\n");
}

Think of it like: Checking if you’ve read the last page of a book.

Meet ferror() — “Did something break?”

ferror() checks if an error happened while reading or writing.

if (ferror(file)) {
    printf("Oops! Something went wrong!\n");
}

Think of it like: Checking if pages are torn or missing.

Using Both Together — The Smart Way

#include <stdio.h>

int main() {
    FILE *file = fopen("data.txt", "r");
    int ch;

    while ((ch = fgetc(file)) != EOF) {
        printf("%c", ch);
    }

    // Now check WHY we stopped
    if (feof(file)) {
        printf("\nFinished reading!\n");
    }
    if (ferror(file)) {
        printf("\nError occurred!\n");
    }

    fclose(file);
    return 0;
}

🎯 Quick Comparison

Clearing Errors with clearerr()

Sometimes you want to try again after an error. Use clearerr() to reset:

clearerr(file);  // Reset error and EOF flags
// Now try reading again!

🗑️ Part 3: remove() — “The Delete Button”

What Does remove() Do?

remove() deletes a file from your computer. Gone. Poof!

Think of it like: Throwing a book in the trash can. It’s gone forever!

How to Use remove()

#include <stdio.h>

int main() {
    if (remove("old_file.txt") == 0) {
        printf("File deleted!\n");
    } else {
        printf("Couldn't delete file!\n");
    }
    return 0;
}

⚠️ Important Rules

Real World Example

// Clean up temporary files
if (remove("temp_data.txt") != 0) {
    perror("Failed to delete");
}

✏️ Part 4: rename() — “The Name Changer”

What Does rename() Do?

rename() changes a file’s name. Like putting a new label on a folder!

Think of it like: Erasing the title of a book and writing a new one.

How to Use rename()

#include <stdio.h>

int main() {
    if (rename("old_name.txt", "new_name.txt") == 0) {
        printf("Renamed successfully!\n");
    } else {
        printf("Rename failed!\n");
    }
    return 0;
}

🎯 rename() Can Also Move Files!

// Move file to a different folder
rename("file.txt", "backup/file.txt");

Common Mistakes to Avoid

🔧 Putting It All Together

Here’s a complete example that uses everything we learned:

#include <stdio.h>

int main() {
    FILE *file;
    int ch;

    // Step 1: Read a file
    file = fopen("input.txt", "r");
    if (file == NULL) {
        perror("Can't open file");
        return 1;
    }

    // Step 2: Read until EOF
    while ((ch = fgetc(file)) != EOF) {
        printf("%c", ch);
    }

    // Step 3: Check what happened
    if (feof(file)) {
        printf("\n[Finished reading]\n");
    }
    if (ferror(file)) {
        printf("\n[Error occurred]\n");
    }

    fclose(file);

    // Step 4: Rename the file
    if (rename("input.txt", "done.txt") == 0) {
        printf("File renamed!\n");
    }

    // Step 5: Delete old backup
    remove("backup.txt");

    return 0;
}

🎓 Summary: Your Error Handling Toolkit

graph TD
    A["Your File"] --> B{Reading?}
    B --> C["Check for EOF"]
    C --> D["feof - End reached?"]
    C --> E["ferror - Error happened?"]
    B --> F{Managing Files?}
    F --> G["remove - Delete it"]
    F --> H["rename - Change name"]

Quick Reference

🌟 You Did It!

You now know how to:

• ✅ Detect when you’ve read everything (EOF)
• ✅ Tell the difference between “finished” and “broken” (feof vs ferror)
• ✅ Delete files safely (remove)
• ✅ Rename and move files (rename)

Remember: Good programmers always check for errors. It’s like wearing a seatbelt—you hope you never need it, but you’re glad it’s there!

Happy coding! 🚀