Set_error_handler function in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP code using set_error_handler?

Consider the following PHP code that sets a custom error handler. What will it output when run?

PHP

<?php
function customError($errno, $errstr) {
    echo "Error caught: [$errno] $errstr\n";
}
set_error_handler('customError');
// Trigger an error
echo $undefinedVar;
?>

A Error caught: [8] Undefined variable: undefinedVar

B Notice: Undefined variable: undefinedVar in script on line 7

C No output

D Fatal error: Uncaught Error: Undefined variable: undefinedVar

💡 Hint

The custom error handler replaces the default error message for notices.

The set_error_handler function sets a user-defined function to handle errors. When the undefined variable is accessed, a notice is triggered. Instead of the default PHP notice, the customError function runs and outputs the formatted message.

🧠 Conceptual

intermediate

Which error types can be handled by set_error_handler?

In PHP, which of the following error types can be caught and handled by a function set with set_error_handler?

A All errors including fatal compile-time errors

B E_NOTICE, E_WARNING, E_USER_ERROR

C E_COMPILE_ERROR, E_CORE_WARNING, E_PARSE

D E_PARSE, E_ERROR, E_CORE_ERROR

💡 Hint

Some errors occur before the script runs and cannot be caught.

set_error_handler can handle runtime errors like notices, warnings, and user-generated errors. It cannot handle parse errors or fatal errors that stop script execution before the handler is set.

🔧 Debug

advanced

Why does this custom error handler not catch the error?

Look at this PHP code. The custom error handler is set, but the error is not caught by it. Why?

PHP

<?php
function myErrorHandler($errno, $errstr) {
    echo "Caught error: $errstr\n";
}
// Intentionally trigger a parse error
set_error_handler('myErrorHandler');
eval('echo "Hello"');
?>

A Parse errors cannot be caught by set_error_handler because they occur before runtime.

B The error handler function name is incorrect.

C eval() suppresses all errors by default.

D The error handler must be set after the eval statement.

💡 Hint

Parse errors happen before the script runs.

Parse errors happen during the compilation phase before the script runs, so set_error_handler cannot catch them. Only runtime errors can be caught.

📝 Syntax

advanced

Which option correctly sets a custom error handler that ignores E_NOTICE errors?

You want to set a custom error handler in PHP that handles all errors except notices (E_NOTICE). Which code snippet does this correctly?

A set_error_handler('handler', E_NOTICE);

B set_error_handler('handler', E_ALL | E_NOTICE);

C set_error_handler('handler', E_ALL & ~E_NOTICE);

D set_error_handler('handler', E_ALL ^ E_NOTICE);

💡 Hint

Use bitwise operators to exclude E_NOTICE.

E_ALL & ~E_NOTICE means all errors except notices. The bitwise AND with the negation of E_NOTICE excludes notices from the handled errors.

🚀 Application

expert

What is the output of this PHP code with nested error handlers?

Analyze this PHP code that sets two error handlers one after another. What will be the output when an undefined variable is accessed?

PHP

<?php
function firstHandler($errno, $errstr) {
    echo "First handler: $errstr\n";
    return false; // Pass to next handler
}
function secondHandler($errno, $errstr) {
    echo "Second handler: $errstr\n";
}
set_error_handler('firstHandler');
set_error_handler('secondHandler');
echo $undefinedVar;
?>

A No output

B First handler: Undefined variable: undefinedVar

C

First handler: Undefined variable: undefinedVar
Second handler: Undefined variable: undefinedVar

D Second handler: Undefined variable: undefinedVar

💡 Hint

The last set_error_handler replaces the previous one.

Only the last error handler set is active. The firstHandler is replaced by secondHandler. So only secondHandler runs and outputs the message.