Opening and closing files - Cheat Sheet & Quick Revision

Recall & Review

beginner

What function is used to open a file in C?

The fopen() function is used to open a file in C. It requires the file name and mode (like "r" for read, "w" for write).

beginner

What does the mode "r" mean when opening a file with fopen()?

The mode "r" means open the file for reading only. The file must exist, or fopen() will return NULL.

beginner

How do you properly close a file in C?

Use the fclose() function and pass the file pointer returned by fopen(). This frees resources and saves changes.

intermediate

What happens if you forget to close a file after opening it?

If you forget to close a file, it can cause memory leaks or data not being saved properly. Always close files to keep your program safe.

beginner

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

fopen() returns NULL if it cannot open the file (for example, if the file does not exist in read mode). Always check for NULL before using the file pointer.

Which function opens a file in C?

A fileopen()

B fopen()

C openfile()

D open()

The correct function to open a file in C is fopen().

What mode should you use with fopen() to write to a file?

A "w"

B "rw"

C "a"

D "r"

Use mode "w" to open a file for writing. It creates the file if it doesn't exist or truncates it if it does.

What does fclose() do?

A Reads data from a file

B Deletes a file

C Writes data to a file

D Closes an open file

fclose() closes an open file and releases resources.

If fopen() fails to open a file, what does it return?

A -1

B 0

C NULL

D false

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

Why should you always close files after opening them?

A To free memory and save data

B To speed up the program

C To delete the file

D To rename the file

Closing files frees memory and ensures data is saved properly.

Explain how to open a file for reading and then close it in C.

Think about the steps: open, check, use, close.

What are the risks of not closing a file after opening it?

Consider what happens inside the computer when files stay open.