In PHP file handling, what is the standard way to open a file for reading or writing?

Introduction / Context:
Reading and writing files is a common task in server side programming. PHP provides simple functions for opening files, reading content, and writing output. This question focuses on the correct function and pattern for opening a file, which is the first step in many file handling operations.

Given Data / Assumptions:

• We want to access a file stored on the server file system.
• The file may be opened in different modes such as read, write, or append.
• The language is PHP, which has a rich set of file system functions.

Concept / Approach:
The standard function for opening a file in PHP is fopen(). It takes at least two arguments: the path to the file and a mode string that specifies how the file should be opened. Common modes include "r" for read only, "w" for write (truncating the file or creating a new one), and "a" for append. fopen() returns a file handle resource that can be used with functions like fread(), fwrite(), and fclose(). Correct error checking after fopen() is important to handle cases where the file cannot be opened due to permissions or missing paths.

Step-by-Step Solution:
Step 1: Recall that fopen() is the main PHP function used to open files.Step 2: Remember the basic signature fopen($filename, $mode); where $mode is a string like "r", "w", or "a".Step 3: Recognise that after opening the file you typically check whether the returned handle is valid before proceeding.Step 4: Compare this with the options and identify which one describes this pattern.Step 5: Option A correctly mentions fopen() and illustrates read and write modes, so it is the correct answer.

Verification / Alternative check:
A small script such as $fh = fopen("data.txt", "r"); if ($fh) { echo fgets($fh); fclose($fh); } shows the basic usage. If the file does not exist and you use mode "r", fopen() returns false and no data is read. Changing the mode to "w" creates or truncates the file, confirming that the mode argument controls file access behaviour.

Why Other Options Are Wrong:
Option B claims that assigning a filename to a variable is enough to open a file, which is not true. Option C refers to an open_file keyword, which does not exist in PHP. Option D incorrectly claims that PHP cannot open files, even though file system functions are widely used in PHP applications.

Common Pitfalls:
Developers sometimes forget to close file handles with fclose(), which can lead to resource leaks in long running scripts. Another pitfall is using the wrong mode, unintentionally truncating files when they mean to append. Always double check the mode string and include error handling to make file operations reliable and safe.

Final Answer:
Use the built in function fopen() with a filename and mode string, such as fopen("data.txt", "r") for reading or fopen("data.txt", "w") for writing.