Verifying Variable Undefinedness in PHP

In PHP, the isset() function is commonly used to determine whether a variable is defined. However, it doesn't explicitly check for undefined variables. For that purpose, we can utilize alternative methods:

1. isset($variable)

The isset() function returns true if the variable exists and has a value other than NULL. If the variable is undefined, it returns false.

Example:

$isTouch = isset($variable);

2. empty($variable)

The empty() function returns true if the variable is false, 0, an empty string, NULL, an empty array, or a variable declared without a value. It can be used to check for undefined variables as well.

Example:

$isTouch = empty($variable);

Note:

• isset() only checks if the variable exists. It doesn't check its value.
• empty() checks both the existence and the falsiness of the variable.
• Both isset() and empty() return true for non-empty string values, even if they contain spaces.