w3resource

PHP: isset() function

isset() function

The isset () function is used to check whether a variable is set or not. If a variable is already unset with unset() function, it will no longer be set. The isset() function return false if testing variable contains a NULL value.

Version:

(PHP 4 and above)

Syntax:

isset(variable1, variable2......) 

Parameter:

Name Description Required /
Optional
Type
variable1 The variable being checked Required Mixed*
Variable2 ...... More variable to be checked. Optional Mixed*

*Mixed: Mixed indicates that a parameter may accept multiple (but not necessarily all) types.

Return value:

TRUE if variable (variable1,variable2..) exists and has value not equal to NULL, FALSE otherwise.

Value Type: Boolean.

Pictorial presentation of PHP isset() function

Pictorial presentation of PHP isset() function

Example:

<?php
$var1 = 'test';
var_dump(isset($var1));
?>

Output :

bool(true) 

View the example in the browser

Practice here online :

See also

PHP Function Reference

Previous: is_string
Next: print_r



PHP: Tips of the Day

PHP - how to create a newline character?

Only double quoted strings interpret the escape sequences \r and \n as '0x0D' and '0x0A' respectively, so you want:

"\r\n"

Single quoted strings, on the other hand, only know the escape sequences \\ and \'.

So unless you concatenate the single quoted string with a line break generated elsewhere (e. g., using double quoted string "\r\n" or using chr function chr(0x0D).chr(0x0A)), the only other way to have a line break within a single quoted string is to literally type it with your editor:

$s = 'some text before the line break
some text after';

Make sure to check your editor for its line break settings if you require some specific character sequence (\r\n for example).

Ref : https://bit.ly/3hcyege