Writing files (fwrite, file_put_contents) in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the fwrite function do in PHP?

The fwrite function writes data to an open file pointer. You must open the file first with fopen, then use fwrite to write content to it.

beginner

How does file_put_contents simplify writing files compared to fwrite?

file_put_contents writes a string directly to a file without needing to open or close the file manually. It is a shortcut for simple file writing tasks.

beginner

What must you do before using fwrite to write to a file?

You must open the file using fopen with the correct mode (like 'w' for write). After writing, you should close the file with fclose.

intermediate

What happens if you use file_put_contents on a file that already exists?

By default, file_put_contents will overwrite the existing file content. You can append instead by passing the FILE_APPEND flag.

beginner

Write a simple PHP code snippet using fwrite to write 'Hello' to a file named 'greet.txt'.

<?php
$fp = fopen('greet.txt', 'w');
fwrite($fp, 'Hello');
fclose($fp);
?>

Which PHP function writes data directly to a file without manually opening it?

A fclose

B fopen

C fwrite

D file_put_contents

file_put_contents writes data directly to a file, handling opening and closing internally.

What mode should you use with fopen to write and overwrite a file?

A 'r'

B 'a'

C 'w'

D 'x'

The 'w' mode opens the file for writing and truncates it to zero length, overwriting existing content.

What does fclose do in file handling?

A Closes an open file pointer

B Writes data to a file

C Reads data from a file

D Deletes a file

fclose closes the file pointer opened by fopen, freeing system resources.

How do you append data to a file using file_put_contents?

A Use the FILE_APPEND flag

B Use the 'w' mode

C Use the 'r' mode

D Use the 'x' mode

Passing the FILE_APPEND flag tells file_put_contents to add data to the end of the file instead of overwriting.

Which of these is the correct order to write to a file using fwrite?

A fwrite, fopen, fclose

B fopen, fwrite, fclose

C fclose, fwrite, fopen

D fopen, fclose, fwrite

You must open the file first, then write, then close it.

Explain how to write text to a file in PHP using fwrite. Include the steps and functions involved.

Think about opening the file, writing, then closing it.

Describe the difference between fwrite and file_put_contents when writing files in PHP.

One needs more steps, the other is simpler for quick writes.

Practice

1. Which PHP function is best for quickly writing a string to a file without manually opening or closing it?

easy

A. fclose

B. fwrite

C. fopen

D. file_put_contents

Solution

1. Step 1: Understand the purpose of file_put_contents

   This function writes data to a file in one step, handling opening and closing automatically.

2. Step 2: Compare with fwrite

   fwrite requires manual file opening and closing, so it's not as quick for simple writes.

3. Final Answer:

   file_put_contents -> Option D

4. Quick Check:

   Quick file write = file_put_contents [OK]

Hint: Use file_put_contents for quick file writes without fopen/fclose [OK]

Common Mistakes:

• Confusing fwrite as a standalone write function
• Thinking fopen writes data
• Assuming fclose writes data

2. Which of the following is the correct syntax to write "Hello" to a file named "greet.txt" using fwrite?

easy

A. $file = fopen('greet.txt'); fwrite($file, 'Hello');

B. $file = fopen('greet.txt', 'w'); fwrite($file, 'Hello'); fclose($file);

C. file_put_contents('greet.txt', 'Hello');

D. fwrite('greet.txt', 'Hello');

Solution

1. Step 1: Check the correct usage of fwrite

   fwrite requires a file handle from fopen opened in write mode.

2. Step 2: Validate the full sequence

   $file = fopen('greet.txt', 'w'); fwrite($file, 'Hello'); fclose($file); opens the file in write mode, writes "Hello", then closes the file properly.

3. Final Answer:

   $file = fopen('greet.txt', 'w'); fwrite($file, 'Hello'); fclose($file); -> Option B

4. Quick Check:

   fopen + fwrite + fclose = correct syntax [OK]

Hint: Always fopen with 'w' before fwrite, then fclose [OK]

Common Mistakes:

• Calling fwrite without fopen file handle
• Missing file mode in fopen
• Not closing the file after writing

3. What will be the output of this PHP code?

$filename = 'data.txt';
file_put_contents($filename, "Line1\n");
$file = fopen($filename, 'a');
fwrite($file, "Line2\n");
fclose($file);
echo file_get_contents($filename);

medium

A. Line2

B. Line1

C. Line1
Line2

D. Error: file not found

Solution

1. Step 1: Analyze file_put_contents call

   This writes "Line1\n" to 'data.txt', creating or overwriting the file.

2. Step 2: Analyze fopen with 'a' mode and fwrite

   Opening in append mode adds "Line2\n" after existing content.

3. Step 3: Read file content with file_get_contents

   It returns both lines concatenated with newlines.

4. Final Answer:

   Line1 Line2 -> Option C

5. Quick Check:

   Append mode adds lines, so both lines appear [OK]

Hint: file_put_contents overwrites; fopen 'a' appends [OK]

Common Mistakes:

• Assuming file_put_contents appends instead of overwrites
• Forgetting 'a' mode appends
• Expecting only last line output

4. Identify the error in this PHP code snippet that tries to write "Test" to "file.txt":

$file = fopen('file.txt', 'r');
fwrite($file, 'Test');
fclose($file);

medium

A. File opened in read mode, cannot write

B. Missing semicolon after fwrite

C. fclose called before fwrite

D. fopen filename missing extension

Solution

1. Step 1: Check fopen mode

   The file is opened in 'r' (read) mode, which does not allow writing.

2. Step 2: Understand fwrite requirements

   Writing requires 'w', 'a', or 'r+' mode; 'r' mode causes error on fwrite.

3. Final Answer:

   File opened in read mode, cannot write -> Option A

4. Quick Check:

   Write needs write mode, not 'r' [OK]

Hint: Open file with 'w' or 'a' to write, not 'r' [OK]

Common Mistakes:

• Using 'r' mode when writing
• Ignoring file mode errors
• Assuming fwrite works on read-only handle

5. You want to save user input lines into a file, but only if the input is not empty or whitespace. Which PHP code snippet correctly writes non-empty trimmed lines to "input.txt" using fwrite?

hard

A. $file = fopen('input.txt', 'w'); foreach ($lines as $line) { if (trim($line) !== '') { fwrite($file, $line . "\n"); } } fclose($file);

B. $file = fopen('input.txt', 'w'); foreach ($lines as $line) { fwrite($file, $line . "\n"); } fclose($file);

C. file_put_contents('input.txt', implode("\n", $lines));

D. $file = fopen('input.txt', 'r'); foreach ($lines as $line) { if ($line) { fwrite($file, $line); } } fclose($file);

Solution

1. Step 1: Check file open mode

   $file = fopen('input.txt', 'w'); foreach ($lines as $line) { if (trim($line) !== '') { fwrite($file, $line . "\n"); } } fclose($file); opens file in 'w' mode, allowing writing and overwriting.

2. Step 2: Validate input filtering

   It uses trim($line) !== '' to skip empty or whitespace-only lines before writing.

3. Step 3: Confirm writing and closing

   Writes each valid line with newline and closes file properly.

4. Final Answer:

   Option A code snippet -> Option A

5. Quick Check:

   Trim check + fwrite + 'w' mode = correct [OK]

Hint: Trim input lines and write only non-empty with fwrite [OK]

Common Mistakes:

• Not trimming lines before writing
• Opening file in 'r' mode when writing
• Using file_put_contents without filtering