PHP
Opening files with fopen()
Learn to open a file in different modes (r, w, a) with fopen().
Opening files with fopen()
file_get_contents() reads the whole file at once; but sometimes you want to process a file step by step, in chunks. For that you first open it with fopen(), then read or write through the returned handle.
For example, $handle = fopen('data.txt', 'r'); opens data.txt in read mode and returns a handle. You then use this handle for later reads or writes.
If fopen() fails it returns false. It is a good habit to check the handle before using it.
Common file modes: r, w, a
fopen() takes three main modes:
'r' — read mode. The cursor is at the start, the file cannot be modified.'w' — write mode. If the file does not exist it is created; if it exists it is truncated and the cursor is at the start.'a' — append mode. If the file does not exist it is created; if it exists the cursor is at the end and the existing content is preserved.
Picking the wrong mode can cause data loss. For example, opening a file with 'w' immediately erases its previous content. Choose the mode carefully.
Exercise Open the file in read mode
First use file_put_contents() to write 'content' into data.txt (given part). Then open the file with fopen() in 'r' mode and store the handle in $handle. If the handle is valid, print a short message with echo.
Show example solution
Write $handle = fopen(__DIR__ . '/data.txt', 'r'); then check with if ($handle) { echo 'File opened'; }.
Example solution:
<?php
// Create the test file
file_put_contents(__DIR__ . '/data.txt', 'content');
// Open the file in read mode
$handle = fopen(__DIR__ . '/data.txt', 'r');
// Print a message if it opened
if ($handle) {
echo 'File opened';
}
Test yourself
-
Which mode opens a file for reading only?
- 'w' mode
- 'a' mode
- 'r' mode
- 'x' mode
Show answer
'r' mode — Correct. 'r' mode opens the file for reading only; no writing is allowed.
-
Open the file in read mode
$handle = fopen('data.txt', ____);
Show answer
$handle = fopen('data.txt', 'r');
-
Match the file modes
- 'r' mode
- Read only
- 'w' mode
- Truncate and write
- 'a' mode
- Append to the end
- fopen()
- Opens the file
Next lesson: fwrite() and fread()
