Writing files (fwrite, file_put_contents) in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP code writing to a file?

Consider this PHP code that writes text to a file. What will be the content of the file example.txt after running this code?

PHP

<?php
$file = fopen('example.txt', 'w');
fwrite($file, "Hello");
fwrite($file, " World");
fclose($file);
?>

A The file contains: Hello\nWorld

B The file contains: HelloWorld

C The file contains: Hello World

D The file is empty

💡 Hint

Remember fwrite writes exactly what you give it without adding spaces.

The fwrite function writes the exact string given. Since "Hello" and " World" are written separately, the file content is concatenated as "Hello World" without any extra characters. Note the space before 'World' is part of the string.

❓ Predict Output

intermediate

What does file_put_contents write to the file?

What will be the content of data.txt after running this PHP code?

PHP

<?php
file_put_contents('data.txt', "Line1\nLine2");
?>

A

Line1
Line2

B Line1 Line2

C Line1\nLine2

D An empty file

💡 Hint

Check how PHP interprets escape sequences inside double quotes.

Inside double quotes, \n is interpreted as a newline character. So the file will contain two lines: 'Line1' and 'Line2' on separate lines.

🔧 Debug

advanced

Why does this fwrite code cause an error?

This PHP code tries to write to a file but causes an error. What is the cause?

PHP

<?php
$file = fopen('output.txt', 'r');
fwrite($file, "Test");
fclose($file);
?>

A fclose must be called before fwrite

B The file 'output.txt' does not exist, causing fwrite to fail

C fwrite requires the file to be opened in binary mode

D fopen mode 'r' opens file for reading only, so fwrite fails

💡 Hint

Check the fopen mode and what it allows.

Opening a file with mode 'r' means read-only. Writing with fwrite is not allowed and causes an error.

🧠 Conceptual

advanced

How does file_put_contents behave with FILE_APPEND flag?

What will be the content of log.txt after running this PHP code twice in a row?

PHP

<?php
file_put_contents('log.txt', "Entry1\n");
file_put_contents('log.txt', "Entry2\n", FILE_APPEND);
?>

A

Entry1
Entry2

B

Entry1
Entry1
Entry2

C

Entry1

D

Entry2

💡 Hint

FILE_APPEND adds content to the end of the file instead of overwriting.

The first call writes 'Entry1\n' overwriting any existing content. The second call appends 'Entry2\n' to the file. So the file contains both entries in order.

❓ Predict Output

expert

What is the number of bytes written by fwrite here?

Given this PHP code, what is the value of $bytes after fwrite runs?

PHP

<?php
$file = fopen('test.txt', 'w');
$bytes = fwrite($file, "Hello\nWorld");
fclose($file);
echo $bytes;
?>

A 12

B 11

C 10

D 5

💡 Hint

Count all characters including the newline.

The string "Hello\nWorld" has 11 characters: 5 letters in 'Hello', 1 newline, and 5 letters in 'World'. fwrite returns the number of bytes written, which is 11.

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