Summary of function usage for judging PHP variables

Unlike other languages, PHP is not a strictly typed language. Basically, this means that developers do not have to explicitly set the type of a variable (number, string, boolean) before using it. Instead, the PHP interpreter automatically detects the type of the variable based on the information stored in the variable. Although this feature makes programming with PHP very easy, it also has an important flaw: when you need to test the type of a variable Languages ​​that handle types more loosely can be a bit confusing. Fortunately, the developers of PHP noticed this and included a toolkit of functions specifically for testing variables and finding out which specific character class category they belong to - also That is, whether they contain strings, integers, objects, or Boolean values.

The more useful functions in this category are listed below, with descriptions and application examples provided. empty($var)
This function is used to check whether the variable is empty (no value or zero value). Use this function to check user input, for example, form variables. Ensure they contain valid data.

<?php 
// returns false 
$var = "hello"; 
echo empty($var) ? "true" : "false"; 
// returns true 
$var = 0000; 
echo empty ($var) ? "true" : "false"; 
?>

<?php 
// returns string 
$var = "hello"; 
echo gettype($var); 
//returns double 
$var = 1000.56; 
echo gettype($var); 
?>

is_bool($var)
This function tests a variable to see if it contains a Boolean value (true/false). Use this function to check if a variable is a Boolean variable.

<?php 
// returns true 
$var = false; 
echo is_bool($var) ? "true" : "false"; 
?>

<?php 
// returns true 
$var = "exception"; 
echo is_string($var) ? "true" : "false"; 
// returns true 
$var = "88408"; 
echo is_string($var) ? "true" : "false"; 
?>

<?php 
// returns true 
$var = "+99.766"; 
echo is_numeric($var) ? "true" : "false"; 
// returns false 
$var = "b00"; 
echo is_numeric($var) ? "true" : "false"; 
?>

is_array($var)
This function tests a variable to see if it is a PHP-related or numerically indexed array. Use this function to check whether a variable is an array before processing it in a loop.

<?php 
// returns true 
$var = array("tiger", "lion", "zebra"); 
echo is_array($var) ? "true" : "false"; 
// returns false 
$var = "zebra"; 
echo is_array($var) ? "true" : "false"; 
?>

<?php 
// returns false 
$var = "aa"; 
echo is_null($var) ? "true" : "false"; 
// returns true 
$var = null; 
echo is_null($var) ? "true" : "false"; 
?>

This function tests a variable to see if it is a PHP object. This function is generally used to test whether a variable is a PHP object before calling a method or accessing
properties.

<?php 
// returns false 
$var = "exception"; 
echo is_object($var) ? "true" : "false"; 
// returns true 
$var = new Exception; 
echo is_object($var) ? "true" : "false"; 
?>

<?php 
// returns true 
$var = "yes"; 
echo isset($var) ? "true" : "false"; 
// returns false 
echo isset($test) ? "true" : "false"; 
?>

a script.

<?php 
$var = array("one", "two", array("red", "green"), new Exception, 467); 
print_r($var); 
?>

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