How to check if a variable is a String in PHP?
Which methods are available in PHP to check if a variable is a String? In this tutorial, we are going to see how to check if a variable is a String in PHP.
is_string()
The function is_string($var) returns whether the passed variable is a String or not:
<?php
var_dump( is_string('hello') ); // true
var_dump( is_string('') ); // true
var_dump( is_string('5') ); // true
var_dump( is_string('false') ); // true
var_dump( is_string(0) ); // false
var_dump( is_string(1) ); // false
var_dump( is_string(5.0) ); // false
var_dump( is_string(true) ); // false
var_dump( is_string(new stdClass()) ); // false
class Test {
public function __toString() {
return 'Test';
}
}
$obj = new Test();
var_dump( is_string($obj) ); // false
var_dump( is_string((string)$obj) ); // true
var_dump( is_string($obj->__toString()) ); // true
?>
Output:
bool(true) bool(true) bool(true) bool(true) bool(false) bool(false) bool(false) bool(false) bool(false) bool(false) bool(true) bool(true)
While in Java a string can also be NULL, this is not possible in PHP. If is_string() returns true, you can be sure that the variable is not NULL.
Test for float parameters
It makes sense to use is_string() to check function parameters:
<?php
function startsWith($str, $start)
{
if (!is_string($str) || !is_string($start))
{
// Error handling(Exception)
throw new Exception('The parameters $str and $start must both be strings.');
}
return (strpos($str, $start)===0);
}
try
{
var_dump(startsWith('StackHowTo', 'Stack')); // true
var_dump(startsWith('Hello', 'llo')); // false
var_dump(startsWith('100', 1)); // Exception
}
catch (Exception $e)
{
echo($e->getMessage());
}
?>
Output:
bool(true) bool(false) The parameters $str and $start must both be strings.
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