PHP errors look intimidating, but they follow one pattern: type, message, file, line.
PHP Fatal error: Uncaught Error: Call to undefined function mb_strlen() in /home/user/domains/yourdomain.co.uk/public_html/lib/text.php:42- Type: Fatal error
- Message: Call to undefined function
mb_strlen() - File:
lib/text.php - Line: 42
Error types, from most to least serious
| Type | Effect | Example cause |
|---|---|---|
| Parse error | Nothing in that file runs | A missing ; or bracket after an edit |
| Fatal error | Script stops — blank page, 500 or critical error | Undefined function, out of memory, uncaught exception |
| Warning | Script continues, but something failed | File not found, division by zero |
| Notice | Script continues; possible bug | Undefined variable or array key |
| Deprecated | Works now, will break in a future version | Old syntax or removed-soon functions |
What to do with each
- Parse and fatal errors break the site. Fix these first.
- Warnings deserve investigation if something isn’t working.
- Notices and deprecations can wait, but plan to address deprecations before upgrading PHP.
Common fatal errors
Call to undefined function→ “Call to undefined function” PHP errorAllowed memory size exhausted→ “Allowed memory size exhausted” PHP errorMaximum execution time exceeded→ “Maximum execution time exceeded” PHP errorCannot modify header information - headers already sent→ “Cannot modify header information - headers already sent”
Where errors go
Visitors shouldn’t see errors. They should be logged. How to find PHP errors (error logs and display_errors)
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