PHP error guide

Call to undefined function create_function: meaning and fix

fatal fatal Affects: PHP 8.0+ Last verified:

Error summary

Replace generated callbacks with closures that capture explicit variables. PHP 8 removed create_function(), which evaluated generated source.

What it means

Replace generated callbacks with closures that capture explicit variables. PHP 8 removed create_function(), which evaluated generated source.

What the error means

This message means that PHP 8 removed create_function(), which evaluated generated source. The exact signature distinguishes call to undefined function create_function from a generic application failure.

Why PHP produces it

The engine or service reports “Call to undefined function create_function” because its required precondition was not met. Replace generated callbacks with closures that capture explicit variables.

PHP version notes

The call to undefined function create_function wording here is based on PHP 8.0+; punctuation and exception class names can differ on older branches or vendor builds.

Most common causes

  • The immediate input or configuration reaches the specific condition: PHP 8 removed create_function(), which evaluated generated source
  • The code path assumes the prerequisite for call to undefined function create_function has already been satisfied.
  • For call to undefined function create_function, development and production differ in version, extension, permissions, paths, or service configuration.
  • An earlier operation returned an unchecked value that is consumed by the line reporting call to undefined function create_function.

Minimal examples

BAD — reproduces the problem

php 
$fn = create_function('$x', 'return $x*2;');

FIXED — safer pattern

php 
$fn = static fn(int $x): int => $x * 2;

Step-by-step diagnosis

  1. Copy the complete “Fatal error: Uncaught Error: Call to undefined function create_function()” text and retain the first application stack frame.
  2. Reproduce call to undefined function create_function in the same SAPI and environment listed for this page.
  3. Before changing call to undefined function create_function, inspect the preceding value or directive and verify its type, path, version, and permissions.
  4. Apply the narrow correction—replace generated callbacks with closures that capture explicit variables—then repeat the original request once.

Fixes

Correct the failing prerequisite

Replace generated callbacks with closures that capture explicit variables

php 
$fn = static fn(int $x): int => $x * 2;

Fail explicitly at the boundary

Validate the condition before the operation that emits call to undefined function create_function, and log a safe diagnostic without credentials or full production paths.

Common mistakes when fixing it

  • Suppressing call to undefined function create_function instead of correcting its upstream condition.
  • Testing call to undefined function create_function only with the CLI binary when the failing request runs under FPM or Apache.
  • Changing a global setting for call to undefined function create_function before confirming the site-specific effective configuration.

How to prevent it

  • Add a focused test that exercises the boundary responsible for call to undefined function create_function.
  • Keep runtime versions, extensions, configuration, and deploy artifacts affecting call to undefined function create_function reproducible.
  • Validate external data and service return values before they can trigger call to undefined function create_function.

Web server / environment notes

cli, fpm, wordpress. The failure occurs where pHP 8 removed create_function(), which evaluated generated source

Tags: cli,fpm,wordpress

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