PHP Errors, Warnings and Notices

When working with PHP, errors fall into a few common categories, each with a different level of severity and impact on how a website behaves.

Understanding these distinctions is important, as some errors will completely halt execution while others are more like alerts, giving developers the chance to fix issues without the site necessarily breaking.

Warnings

A warning indicates that something has gone wrong, but it is not serious enough to stop the script from running. For example, if a file you are trying to include is missing, PHP will display a warning. The rest of the script will usually continue to execute. This means a page may still load, though some functionality could be missing or behave unexpectedly.

Notices

Notices are the least severe. They are often triggered when PHP encounters code that might work but is potentially problematic. A common example is using a variable before it has been defined. Notices do not stop the execution of a script and in many cases users will not even realise they exist, particularly on a live site where error reporting is turned off. They are, however, a useful tool during development as they highlight coding practices that could cause future issues.

Fatal Errors

Fatal errors are the most serious type. They occur when PHP encounters a problem it cannot recover from, such as calling a function that does not exist or exhausting the memory limit. Unlike warnings and notices, fatal errors will immediately stop the execution of the script. If a fatal error occurs, the website will not continue loading beyond the point where the error was triggered, often leaving the user with a blank page or an error message.

Parse Errors

A parse or syntax error occurs when PHP cannot understand the code because of incorrect syntax. This might be something as simple as a missing semicolon, an unmatched bracket, or a mistyped keyword. Unlike warnings or notices, a parse error happens before the script even begins to run, because PHP fails to interpret the code properly in the first place. As a result, parse errors will always stop a website from working on the affected page. No part of the script beyond the point of the error will be executed, and in many cases the page will display nothing more than a raw error message (if error reporting is enabled).

In summary, notices and warnings allow the script to continue running, though often with reduced functionality or unexpected behaviour. Fatal errors and parse errors, on the other hand, will always stop execution and prevent the page from displaying correctly.