Checks whether every byte is an ASCII letter or digit.
What Is ctype_alnum() in PHP?
Checks whether every byte is an ASCII letter or digit.
Its syntax is:
ctype_alnum(mixed $text): boolParameters:
$text— Accepted as mixed; required argument.
Return type: bool. An empty string returns false. These functions examine bytes and locale classification, not full Unicode character properties.
Availability: Requires the ctype extension, normally bundled with PHP.
Example 1: Basic Usage
<?php
var_dump(ctype_alnum("A42"));
Output:
bool(true)An empty string returns false. These functions examine bytes and locale classification, not full Unicode character properties.
Example 2: A Different Input
<?php
var_dump(ctype_alnum("A-2"));
Output:
bool(false)An empty string returns false. These functions examine bytes and locale classification, not full Unicode character properties.
Practical Example: Applying It in a Program
<?php
$samples = ["A1", "AB", "12", "A-1"]; foreach ($samples as $sample) { echo $sample . ": " . (ctype_alnum($sample) ? "yes" : "no") . PHP_EOL; }
Output:
A1: yes
AB: yes
12: yes
A-1: noAn empty string returns false. These functions examine bytes and locale classification, not full Unicode character properties.
Important Behavior and Edge Cases
- Key behavior: An empty string returns false. These functions examine bytes and locale classification, not full Unicode character properties.
- Environment: Requires the ctype extension, normally bundled with PHP.
Comparison With Related Functions
| Function | Purpose |
|---|---|
ctype_alnum() | Checks whether every byte is an ASCII letter or digit. |
preg_match() | preg_match() evaluates a regular-expression pattern; ctype_* functions test every byte against a predefined character class. |
Common Beginner Mistakes
| Mistake | Correct Approach |
|---|---|
| Ignoring this behavior: An empty string returns false | An empty string returns false. These functions examine bytes and locale classification, not full Unicode character properties. |
Key Takeaways
- Checks whether every byte is an ASCII letter or digit.
- An empty string returns false. These functions examine bytes and locale classification, not full Unicode character properties.
- Requires the ctype extension, normally bundled with PHP.
Summary: An empty string returns false. These functions examine bytes and locale classification, not full Unicode character properties.