How to Identify Undefined Variables in PHP?

Identifying Undefined Variables in PHP

In PHP, the isset() function allows you to check if a variable has been set, but it does not distinguish between undefined and null values. To explicitly check for undefined variables, similar to the JavaScript statement document.createTouch !== undefined, you can employ the following approach:

<code class="php">$isTouch = isset($variable);</code>

This expression returns true if $variable is defined, and false otherwise. However, it's important to note that isset() considers a variable defined if it has been set to any value other than NULL.

If you want to check specifically for false, 0, or other values that may be considered "false-like" in PHP, you can use the empty() function:

<code class="php">$isTouch = empty($variable);</code>

empty() returns true for the following cases:

• Empty string (``)
• Integer 0
• Float 0.0
• String "0"
• NULL
• FALSE
• Empty array
• Variables declared but not assigned

By combining isset() and empty(), you can determine whether a variable is undefined or has a false-like value:

<code class="php">$isTouch = !isset($variable) || empty($variable);</code>

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