PHP Error: "Can't use function return value in write context"

This puzzling PHP error occurs when trying to use a function return value in a write context. Specifically, the error arises when you attempt to use a function's return value in a conditional statement, such as an if statement.

The source of the error lies in a PHP language construct called "write context." Write context refers to code that modifies a variable or performs some kind of output. In the case of the "Can't use function return value in write context" error, the function return value is not a suitable input for the write context because it is a language construct rather than a variable.

To resolve this error, you should use a variable to hold the function return value before using it in the write context. For instance, instead of writing:

if (isset($_POST('sms_code') == TRUE ) {

You should write:

$sms_code_isset = isset($_POST('sms_code') == TRUE );
if ($sms_code_isset) {

By separating the function call from the write context, you avoid the error and ensure that the code executes correctly.