set_error_handler()在PHP中用於自定義錯誤處理，可捕獲非致命錯誤如E_WARNING、E_NOTICE等，但無法處理E_ERROR等致命錯誤。 1.其功能包括替換默認錯誤處理、格式化消息、日誌記錄及屏蔽生產(chǎn)環(huán)境特定錯誤；2.自定義函數(shù)需至少接收錯誤級別和消息參數(shù)，並可通過返回true阻止內(nèi)置處理器執(zhí)行；3.默認不捕獲E_ERROR、E_PARSE等致命錯誤，需結(jié)合register_shutdown_function()與error_get_last()處理；4.實踐建議包含日誌記錄、忽略通知、使用對象方法作為處理器及生產(chǎn)環(huán)境避免直接輸出錯誤。

When you're working with PHP and want more control over how errors are handled, set_error_handler() is the tool to use. It lets you define a custom function that will take over when PHP errors occur — like notices, warnings, and other non-fatal errors (but not fatal errors like parsing mistakes).

Here's how to get started.

What set_error_handler() does

The set_error_handler() function allows you to replace PHP's default error handler with your own. You pass it a callback function, and from then on, any eligible error will be passed to your function instead of being displayed or logged the usual way.

You can use this to:

• Format error messages differently
• Log errors in a custom format or location
• Handle recoverable errors gracefully
• Hide certain types of errors in production

Just remember: it won't catch fatal errors like E_PARSE or E_COMPILE_ERROR .

How to define a custom error handler function

Your error handler needs to accept at least two parameters — the error level and the message. Optionally, it can also receive the file name, line number, and the context (an array of variables from the error point).

 function myErrorHandler($errno, $errstr, $errfile, $errline) {
    echo "<b>Custom error:</b> [$errno] $errstr<br>";
    echo "Occurred in $errfile on line $errline";
    return true; // This tells PHP not to execute the built-in handler
}

Then register it:

 set_error_handler("myErrorHandler");

Now, any notice, warning, or similar error will go through your function.

Which errors are caught (and which aren't)

By default, set_error_handler() catches most non-fatal errors, such as:

• E_WARNING
• E_NOTICE
• E_USER_WARNING
• E_USER_NOTICE
• And others — you can find the full list in PHP docs

But it won't catch:

• E_ERROR (fatal run-time errors)
• E_PARSE (parse errors)
• E_CORE_ERROR (PHP startup errors)

These are too severe for a user-defined handler to manage safely.

If you want to handle fatal errors, you'll need to use register_shutdown_function() and inspect the output of error_get_last() .

Some practical tips for using custom error handlers

• Log errors : Use error_log() inside your handler to write to a log file.
• Ignore some errors : Maybe you don't care about E_NOTICE . Your handler can check $errno and decide whether to do anything.
• Use object methods : If you're working in OOP code, you can pass an array like [$object, 'method'] as the handler.
• Restore default behavior : Call restore_error_handler() if you want to revert temporarily.
• Don't display errors in production : In live environments, avoid echoing errors directly — just log them.

Example of ignoring notices:

 function myErrorHandler($errno, $errstr) {
    if ($errno === E_NOTICE) {
        return;
    }
    error_log("Error [$errno] $errstr");
}

That's basically it

Once you've set up your handler, PHP will route appropriate errors through it. It's a simple but powerful way to improve debugging or tailor error responses for different environments. Just make sure your handler doesn't throw its own errors — that could lead to infinite loops or crashes.

So yes, it's not complicated — but there are a few gotchas worth keeping in mind.

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