How to Check for Undefined Values in PHP

Determining Undefined Values in PHP

In PHP, unlike JavaScript, the isset() function is not solely used to check if a variable is undefined. It verifies whether a variable is declared and not explicitly set to NULL. To address the question of checking for undefined values, consider the following solutions:

• isset() Function:

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

  This will return true if the variable is defined, and false if it's undefined or set to NULL.

• Empty() Function:

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

  empty() further verifies that a variable is undefined or contains false, 0, 0.0, "0", NULL, an empty array, or a declared variable without a value.

Note:

• isset() returns true if the variable exists and has a value other than NULL.

• empty() works for the following values:

  • "" (empty string)
  • 0 (integer)
  • 0.0 (float)
  • "0" (string)
  • NULL
  • FALSE
  • array() (empty array)
  • $var; (variable declared without a value)

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