Writing to files in C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What function is used to open a file for writing in C?

The fopen() function is used to open a file. To open a file for writing, you use fopen(filename, "w").

beginner

How do you write a string to a file in C?

You use the fprintf() or fputs() functions. For example, fprintf(file, "%s", "Hello") writes the string "Hello" to the file.

beginner

What must you always do after finishing writing to a file?

You must close the file using fclose(file) to save changes and free resources.

intermediate

What happens if you open a file with mode "w" and the file already exists?

The existing file is cleared (emptied) before writing starts. If the file does not exist, a new file is created.

beginner

How can you check if a file was opened successfully?

After calling fopen(), check if the returned pointer is NULL. If it is NULL, the file did not open successfully.

Which mode opens a file for writing and clears its contents if it exists?

A "w"

B "r"

C "a"

D "r+"

Mode "w" opens a file for writing and clears existing content or creates a new file.

What does fclose() do in file handling?

A Deletes the file

B Opens the file for reading

C Reads data from the file

D Closes the file and saves changes

fclose() closes the file and ensures all data is saved properly.

Which function writes formatted text to a file?

A fread()

B fprintf()

C fclose()

D fopen()

fprintf() writes formatted text to a file.

How do you check if fopen() failed to open a file?

A Check if the file exists

B Check if the file size is zero

C Check if the returned pointer is NULL

D Check if the file is empty

If fopen() returns NULL, it means the file could not be opened.

Which function writes a string to a file without formatting?

A fputs()

B fprintf()

C fread()

D fclose()

fputs() writes a string directly to a file without formatting.

Explain the steps to write text to a file in C.

Think about opening, writing, and closing the file.

What happens if you open a file with "w" mode and the file already exists?

Consider how "w" mode treats existing files.