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In PHP programming, it's often necessary to determine whether a string is a number. This requirement is especially common in scenarios like data validation, user input handling, and form verification. PHP offers a very handy built-in function called is_numeric, which can quickly check if a variable is a number or a numeric string.
This article will provide a detailed introduction to how to use the is_numeric function, along with some practical examples to help you better understand and utilize this function.
is_numeric is a PHP function used to detect whether a variable is a number or a numeric string. It returns a boolean value: true or false.
If the variable is an integer, a float, or a string made up of numbers (including those with decimal points, positive/negative signs, or scientific notation), the function returns true.
Otherwise, it returns false.
Function definition:
bool is_numeric ( mixed $var )
The parameter $var is the variable you want to check.
Here are some code examples demonstrating how to use is_numeric:
<?php
$values = [
"123",
"12.3",
"-123",
"1e10",
"abc",
"123abc",
"",
" 123 ",
null,
123,
12.3
];
<p>foreach ($values as $value) {<br>
if (is_numeric($value)) {<br>
echo "'$value' is a number or numeric string\n";<br>
} else {<br>
echo "'$value' is not a numeric string\n";<br>
}<br>
}<br>
?><br>
Output:
'123' is a number or numeric string
'12.3' is a number or numeric string
'-123' is a number or numeric string
'1e10' is a number or numeric string
'abc' is not a numeric string
'123abc' is not a numeric string
'' is not a numeric string
' 123 ' is not a numeric string
'' is not a numeric string
'123' is a number or numeric string
'12.3' is a number or numeric string
From the results, you can see that is_numeric recognizes integers, floats, negative numbers, and numbers in scientific notation, but it does not support strings containing spaces or mixed letters.
<?php
$user_input = "45.67";
<p>if (is_numeric($user_input)) {<br>
echo "The input is a valid number";<br>
} else {<br>
echo "The input is not a number, please try again";<br>
}<br>
?><br>
Assuming you get a parameter from the URL, you need to check if the parameter is numeric to prevent illegal injection:
<?php
$id = $_GET['id'] ?? '';
<p>if (is_numeric($id)) {<br>
echo "Valid ID: " . intval($id);<br>
} else {<br>
echo "Invalid ID parameter";<br>
}<br>
?><br>
Note here that while is_numeric checks for numeric strings, you can further process the value with intval or type casting if you need an integer.
is_numeric will recognize strings with positive/negative signs, decimal points, or scientific notation as numbers, for example, -3.14 and +1e3 both return true.
Empty strings, strings with only spaces, and alphanumeric mixed strings will return false.
If you need to check whether a variable is a pure integer, you can use ctype_digit, but note it only supports unsigned numeric strings.
For stricter checks of floats or integers, you can combine filter_var with regular expressions.
is_numeric is a simple and efficient PHP function to determine if a variable is a number or numeric string. It is suitable for quickly validating user input or variable types and is very practical in many scenarios. Understanding its behavior and edge cases helps you write more robust code.
If you are working on numeric validation, it is recommended to prioritize using is_numeric, combined with other functions like intval and floatval for further data processing.
