Php debugging
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The document outlines PHP debugging techniques, detailing various message types such as notices, warnings, and errors, including their implications during script execution. It discusses PHP error levels, error management practices, and settings for logging and displaying errors, highlighting best practices for development environments. Additionally, it explains the use of backtracing for debugging in complex structures, providing essential information for effective PHP debugging.
Php debugging
- 2. PHP MESSAGE TYPES • Notice – not a best coding practice • Warning – will probably cause errors upon execution • Error – fatal (crash) • Occur when script is interpreted (no execution - e.g., “The white screen of death”), or at script execution (run-time error halts execution)
- 3. COMMON PHP ERROR LEVELS Referenced by constants representing bit level integers to the interpreter • E_ERROR – fatal run-time error (crash) • E_WARNING – run-time warning • E_NOTICE – run-time notice • E_STRICT – interpretation-time notice • E_DEPRECATED – run-time – will not work in future PHP versions • E_ALL – all notices, warnings, and errors
- 4. DISPLAYING ERRORS • error_reporting – sets level via constant • Default: all except E_NOTICE • display_errors – displays error to users (only use in development environment) • 1 or 0 – default is 1
- 6. SCRIPT LEVEL ERROR MANAGEMENT
- 7. LOGGING ERRORS • log_errors – toggle error logging • Default: off • log_errors_max_len – length of error message in bytes • default: 1024 • 0 is unlimited • error_log – full path to log file • default: NULL (goes to server error log; not a best practice) • set log file path outside of the web root
- 8. DISPLAYING ERRORS • error_reporting – sets level via constant • Default: all except E_NOTICE • display_errors – displays error to users (only use in development environment) • 1 or 0 – default is 1
- 10. DEBUG_BACKTRACE • backtrace – sequence of function/method calls • invaluable in debugging frameworks/complex structures • returns associative array – keyed in ascending order • lowest number - last execution • each contains function/method, line number, file, class, object, and arguments!
Editor's Notes
- #4: E_ERROR – out of memory is a common oneE_NOTICE – something is probably wrong; accessing a variable that is undefined or an undefined array index – useisset() for good logicE_STRICT – old or sloppy coding, reinforces forward compatibility – e.g., mixing scopes – statically calling a non-static method.E_DEPRECATED – split() function and creating objects by reference (not needed in PHP 5)
- #7: If there is a fatal error in the script, php.ini level error reporting supercedes the script
- #10: E_USER_NOTICE – default for trigger_errorE_USER_WARNINGE_USER_ERROR – stops execution