Reading from files in C - Cheat Sheet & Quick Revision

Recall & Review

beginner

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

The fopen() function is used to open a file. To open a file for reading, use fopen(filename, "r").

beginner

How do you read a single character from a file in C?

Use the fgetc() function. It reads one character from the file and returns it as an int.

intermediate

What does fgets() do when reading from a file?

fgets() reads a line or up to a specified number of characters from a file into a string, stopping at a newline or EOF.

beginner

Why should you always check the return value of fopen()?

Because fopen() returns NULL if the file cannot be opened (e.g., file does not exist or no permission). Checking prevents errors later.

beginner

How do you properly close a file after reading in C?

Use the fclose() function with the file pointer to close the file and free resources.

Which mode should you use with fopen() to read a file?

A "r"

B "w"

C "a"

D "rw"

Use "r" mode to open a file for reading only.

What does fgetc() return when it reaches the end of a file?

A -1

B EOF

C NULL

D 0

fgetc() returns EOF (usually -1) when it reaches the end of the file.

Which function reads a whole line from a file into a string?

A fgetc()

B fprintf()

C fread()

D fgets()

fgets() reads a line or up to a specified number of characters from a file.

What should you do if fopen() returns NULL?

A Handle the error, e.g., show a message and stop reading

B Ignore it and continue

C Try to write to the file

D Close the file pointer

If fopen() returns NULL, the file could not be opened, so you should handle the error.

Which function closes a file in C?

A fileclose()

B close()

C fclose()

D endfile()

fclose() closes the file and releases resources.

Explain the steps to read text from a file in C.

Think about opening, reading, checking errors, and closing.

What are common errors to watch for when reading files in C?

Consider what can go wrong at each step.