File open modes in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP code when opening a file in 'r' mode?

Consider the following PHP code snippet. What will it output if the file 'example.txt' exists and contains the text 'Hello World'?

PHP

<?php
$handle = fopen('example.txt', 'r');
$content = fread($handle, 5);
echo $content;
fclose($handle);
?>

A World

B Error: Cannot open file

C Hello World

D Hello

💡 Hint

The 'r' mode opens the file for reading from the beginning.

The fread function reads 5 bytes from the file starting at the beginning, so it outputs 'Hello'.

❓ Predict Output

intermediate

What happens when opening a non-existent file in 'r' mode?

What will the following PHP code output if 'nofile.txt' does not exist?

PHP

<?php
$handle = fopen('nofile.txt', 'r');
if (!$handle) {
    echo 'Failed to open file';
} else {
    echo 'File opened';
}
?>

A File opened

B Failed to open file

C Warning: fopen(): failed to open stream: No such file or directory

D Empty output

💡 Hint

The 'r' mode requires the file to exist.

Opening a non-existent file in 'r' mode returns false, so the code prints 'Failed to open file'.

❓ Predict Output

advanced

What is the output when writing to a file opened in 'w' mode?

Given the file 'data.txt' contains 'Old Data', what will be the content of the file after running this PHP code?

PHP

<?php
$handle = fopen('data.txt', 'w');
fwrite($handle, 'New Data');
fclose($handle);
$contents = file_get_contents('data.txt');
echo $contents;
?>

A New Data

B Error: Cannot write to file

C Old DataNew Data

D Old Data

💡 Hint

The 'w' mode truncates the file before writing.

Opening a file in 'w' mode clears its contents, so after writing 'New Data', the file contains only that.

❓ Predict Output

advanced

What will be the output when appending to a file with 'a' mode?

If 'log.txt' initially contains 'Line1\n', what will be the content after running this PHP code?

PHP

<?php
$handle = fopen('log.txt', 'a');
fwrite($handle, 'Line2\n');
fclose($handle);
$contents = file_get_contents('log.txt');
echo $contents;
?>

A

Line1
Line2

B

Line2

C Line1

D Error: Cannot append to file

💡 Hint

The 'a' mode adds data to the end of the file without deleting existing content.

The 'a' mode appends 'Line2\n' after the existing 'Line1\n', so the file contains both lines.

🧠 Conceptual

expert

Which file open mode allows reading and writing without truncating the file?

In PHP, which file open mode lets you read and write to a file without deleting its existing content at open?

A 'x+'

B 'w+'

C 'r+'

D 'a+'

💡 Hint

One mode opens the file for reading and writing but does not clear it.

'r+' opens the file for reading and writing starting at the beginning without truncating the file. 'w+' truncates the file. 'a+' opens for reading and writing but places the pointer at the end for writing. 'x+' creates a new file and fails if it exists.

Practice

1. Which PHP file open mode allows you to read from a file without changing its contents?

easy

A. r - Open for reading only

B. w - Open for writing only

C. a - Open for appending

D. x - Create and open for writing

Solution

1. Step 1: Understand the purpose of each mode

   r mode opens a file for reading only, without modifying it. Other modes allow writing or creating files.

2. Step 2: Match the mode to the requirement

   Since the question asks for reading without changing, r is the correct mode.

3. Final Answer:

   r - Open for reading only -> Option A

4. Quick Check:

   Read only = r [OK]

Hint: Read only mode is just 'r' in PHP file functions [OK]

Common Mistakes:

• Choosing 'w' which overwrites the file
• Confusing 'a' (append) with read mode
• Using 'x' which creates a new file

2. Which of the following is the correct syntax to open a file for writing in PHP?

easy

A. fopen('file.txt', 'r')

B. fopen('file.txt', 'a')

C. fopen('file.txt', 'rw')

D. fopen('file.txt', 'w')

Solution

1. Step 1: Recall the mode for writing

   The mode 'w' opens a file for writing and truncates it if it exists.

2. Step 2: Check syntax correctness

   fopen('file.txt', 'w') is the correct syntax to open for writing.

3. Final Answer:

   fopen('file.txt', 'w') -> Option D

4. Quick Check:

   Write mode = 'w' [OK]

Hint: Use 'w' to open file for writing in fopen [OK]

Common Mistakes:

• Using 'r' which is read-only
• Using 'rw' which is invalid in PHP
• Confusing 'a' (append) with write

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

$file = fopen('test.txt', 'a');
fwrite($file, "Hello\n");
fclose($file);
echo file_get_contents('test.txt');

medium

A. Hello

B. Empty output

C. Error: Cannot write to file

D. olleH

Solution

1. Step 1: Understand the 'a' mode effect

   Mode 'a' opens the file for appending, so "Hello\n" (string with actual newline) is added at the end.

2. Step 2: Check output of file_get_contents

   It reads the whole file content including the newline, and echo prints it with the newline interpreted.

3. Final Answer:

   Hello -> Option A

4. Quick Check:

   "Hello\n" adds a newline, so output is Hello followed by newline [OK]

Hint: Append adds 'Hello\n'; echo shows Hello with newline [OK]

Common Mistakes:

• Thinking '\n' becomes literal backslash-n
• Expecting 'Hello' without newline
• Assuming error without write permission

4. Identify the error in this PHP code snippet:

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

medium

A. Missing file path

B. File not closed properly

C. Cannot write to a file opened in 'r' mode

D. fwrite syntax is incorrect

Solution

1. Step 1: Check file open mode

   The file is opened in 'r' mode which is read-only and does not allow writing.

2. Step 2: Understand fwrite limitation

   Calling fwrite on a read-only file causes an error because writing is not permitted.

3. Final Answer:

   Cannot write to a file opened in 'r' mode -> Option C

4. Quick Check:

   Write needs 'w' or 'a' mode [OK]

Hint: Write only works if file opened with 'w' or 'a' [OK]

Common Mistakes:

• Ignoring mode restrictions
• Assuming fclose fixes write errors
• Confusing syntax errors with mode errors

5. You want to open a file in PHP to read and write without truncating it, and create it if it doesn't exist. Which mode should you use?

hard

A. w+

B. a+

C. r+

D. x+

Solution

1. Step 1: Understand each mode's behavior

   r+ reads/writes but fails if file missing; w+ truncates file; a+ reads/writes, creates if missing, appends writes; x+ creates new file only.

2. Step 2: Match requirements

   We want read/write, no truncation, and create if missing. a+ fits all: it opens for reading and appending, creates file if missing, and does not truncate.

3. Final Answer:

   a+ -> Option B

4. Quick Check:

   Read/write + create + no truncate = a+ [OK]

Hint: Use 'a+' to read/write and create without truncating [OK]

Common Mistakes:

• Choosing 'r+' which fails if file missing
• Choosing 'w+' which truncates file
• Confusing 'x+' which fails if file exists