Writing files (fwrite, file_put_contents) in PHP - Step-by-Step Execution

Concept Flow - Writing files (fwrite, file_put_contents)

Open file with fopen or use file_put_contents

↓

Write data to file

↓

Check if write succeeded

↓

Close file if fopen used

↓

End

This flow shows how PHP writes data to a file using fopen/fwrite or file_put_contents, then closes the file if needed.

Execution Sample

PHP

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

This code opens a file for writing, writes 'Hello' with a newline, then closes the file.

Execution Table

Step	Action	Function Call	Result	File State
1	Open file for writing	fopen('test.txt', 'w')	File handle resource	File opened, empty content
2	Write string to file	fwrite(file handle, "Hello\n")	6 bytes written	File contains 'Hello\n'
3	Close file	fclose(file handle)	true	File closed, content saved
4	End	-	-	File closed, content saved

💡 File closed after writing, data saved to 'test.txt'

Variable Tracker

Variable	Start	After fopen	After fwrite	After fclose
$file	null	resource (file handle)	resource (file handle)	null

Key Moments - 3 Insights

Why do we need to close the file after writing?

Closing the file with fclose ensures all data is saved and resources are freed, as shown in step 3 of the execution_table.

What happens if fopen fails to open the file?

If fopen fails, it returns false instead of a resource. You should check this before calling fwrite to avoid errors.

How is file_put_contents different from fopen/fwrite?

file_put_contents combines opening, writing, and closing in one call, simplifying the process as it handles all steps internally.

Visual Quiz - 3 Questions

Look at the execution_table, what is the file state after step 2?

A File is closed and empty

B File is open and contains 'Hello\n'

C File is open but empty

D File is closed and contains 'Hello\n'

💡 Hint

Check the 'File State' column in row for step 2 in execution_table

At which step is the file handle resource no longer available?

A Step 3

B Step 2

C Step 4

D Step 1

💡 Hint

Look at variable_tracker for $file after fclose in step 4

If we replace fopen/fwrite/fclose with file_put_contents, how many steps in execution_table would be combined?

A 3 steps

B 2 steps

C 1 step

D 4 steps

💡 Hint

file_put_contents does opening, writing, and closing in one call, combining steps 1, 2, and 3

Concept Snapshot

PHP file writing:
- fopen('file', 'w') opens file for writing
- fwrite(handle, data) writes data
- fclose(handle) closes file
- file_put_contents('file', data) does all in one
Always close files to save data and free resources.

Full Transcript

This lesson shows how PHP writes data to files using fopen, fwrite, and fclose functions, or the simpler file_put_contents function. First, fopen opens the file and returns a handle. Then fwrite writes the string data to the file. Finally, fclose closes the file to save changes. Alternatively, file_put_contents does all these steps in one call. Closing the file is important to ensure data is saved and resources are freed. The execution table traces each step and the file's state. The variable tracker shows how the file handle changes from null to resource and back to null after closing. Key moments clarify why closing is needed, what happens if fopen fails, and how file_put_contents simplifies writing. The quiz tests understanding of file state after writing, when the handle is closed, and how steps combine with file_put_contents.

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