In PHP, what are the main types of errors (or error levels) that can occur during script execution?

Introduction / Context:
During PHP development, scripts can fail or misbehave due to various types of errors. PHP categorizes these problems into several error levels that indicate their severity and when they occur. Knowing the main error types helps developers quickly diagnose issues, configure error reporting appropriately, and understand log messages in development and production environments. Interviewers often ask about error types to ensure candidates can distinguish between syntax errors, runtime fatal errors, warnings, and notices.

Given Data / Assumptions:

• We are dealing with standard PHP error reporting levels.
• We want a conceptual grouping, not every constant, but the main categories developers encounter.
• PHP scripts can fail to parse or fail at runtime due to missing functions, invalid operations, or other issues.
• The question is asking for types such as parse errors, fatal errors, warnings, and notices.

Concept / Approach:
In PHP, a parse error occurs when the script contains invalid syntax and cannot be compiled; the script will not run at all. Fatal errors occur at runtime when PHP encounters a situation it cannot handle, such as calling an undefined function or running out of memory; execution stops immediately. Warnings signal non fatal issues, like including a missing file, but the script continues to execute after the warning. Notices are even less severe; they highlight possible issues, such as using an undefined variable, but they do not stop execution. PHP has many specific error constants, but these four categories represent the commonly discussed types.

Step-by-Step Solution:
Step 1: Define a parse error (E_PARSE) as a compile time error caused by syntax mistakes such as missing semicolons or unmatched brackets, preventing the script from running. Step 2: Define a fatal error (E_ERROR or E_CORE_ERROR) as a runtime error that stops the script immediately, often due to calling an undefined function, including a missing class, or running into memory limits. Step 3: Define a warning (E_WARNING) as a non fatal runtime error that reports a problem like failing to include a file or opening a resource but allows the script to continue executing. Step 4: Define a notice (E_NOTICE) as a mild message that indicates possible issues, such as using an undefined variable or relying on uninitialized values, which does not stop the script. Step 5: Group these as the main error categories that PHP developers need to understand when reading logs and configuring error_reporting levels.

Verification / Alternative check:
The PHP manual documents many error constants, including E_PARSE, E_ERROR, E_WARNING, and E_NOTICE, and describes their semantics. Testing scripts with deliberate syntax mistakes produces parse errors that prevent execution. Intentionally calling a missing function triggers a fatal error. Including a non existent file, if done with include instead of require, generates a warning, while using an undefined variable produces a notice. Observing these behaviours in practice confirms the conceptual categories described above.

Why Other Options Are Wrong:
Option B is incorrect because PHP clearly distinguishes multiple error types; it is not limited to a single generic error. Option C is wrong because PHP error reporting is not limited to database or network problems; it also reports syntax and runtime issues in the PHP code itself. Option D is incorrect because PHP errors are about PHP code execution, not malformed HTML; while browsers may react to malformed HTML, that is not reported as a PHP error.

Common Pitfalls:
A common pitfall is disabling notices and warnings in production without fixing underlying issues, which can hide bugs or unexpected behaviour. Another mistake is leaving display_errors enabled in production, exposing error details to users and potential attackers. Best practice is to show detailed errors only in development, log errors in production, and handle different error levels appropriately with proper error_reporting configuration and custom error handlers where needed.

Final Answer:
PHP commonly categorizes errors into parse errors, fatal errors, warnings, and notices, representing different severity levels and helping developers diagnose and manage issues in their scripts.