Error handling in files in C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of error handling when working with files in C?

Error handling helps detect and respond to problems like missing files, permission issues, or read/write errors to prevent program crashes and data loss.

beginner

Which function is commonly used to open a file and how do you check if it failed?

The fopen() function opens a file. If it returns NULL, it means the file could not be opened, indicating an error.

intermediate

How can you get more information about the error after a file operation fails?

You can use the global variable errno and functions like perror() or strerror() to get a human-readable error message.

beginner

What should you always do after finishing file operations?

Always close the file using fclose() to free resources and avoid data corruption.

beginner

Show a simple C code snippet that opens a file for reading and handles the error if the file does not exist.

#include int main() { FILE *file = fopen("data.txt", "r"); if (file == NULL) { perror("Error opening file"); return 1; } // File operations here fclose(file); return 0; }

What does fopen() return if it fails to open a file?

A NULL

B 0

C -1

D A file pointer

fopen() returns NULL when it cannot open the file.

Which function prints a descriptive error message related to the last file operation?

A printf()

B perror()

C fclose()

D fopen()

perror() prints a message describing the last error.

Why should you always call fclose() after finishing file operations?

A To open the file again

B To check for errors

C To delete the file

D To free resources and save data properly

fclose() frees resources and ensures data is saved correctly.

What global variable holds the error code after a failed file operation?

A errno

B error_code

C file_error

D status

errno stores the error code after a failure.

If fopen() returns NULL, what is the best next step?

A Ignore and continue

B Call <code>fclose()</code>

C Use <code>perror()</code> to print the error and handle it

D Try to write to the file

You should print the error with perror() and handle the failure properly.

Explain how to safely open a file in C and handle the case when the file cannot be opened.

Think about checking the return value of fopen and printing an error message.

Describe why closing a file with fclose is important after file operations.

Consider what happens if you don't close a file properly.