PHP Development Troubleshooting
Diagnostic solutions for PHP fatal errors, undefined functions, PDO, and syntax bugs. (11 Articles)
PHP Undefined Function Error: Causes, Diagnostics, and Complete Solutions
The PHP fatal error "Call to undefined function [name]()" occurs when the Zend Engine attempts to invoke an identifier that has not been declared. The root causes range from simple typographical errors and missing file inclusions to disabled PHP extensions in php.ini and namespace resolution failures.
How to Fix PHP Database Connection Errors: PDO and MySQLi Solutions
PHP database errors such as "SQLSTATE[HY000] [2002] Connection refused" or "Access denied for user" stem from invalid database credentials, specifying "localhost" instead of 127.0.0.1 (socket vs TCP/IP), stopped MySQL daemons, or unhandled PDO exceptions leaking sensitive passwords.
How to Fix PHP Syntax Errors: A Beginner's Diagnostic & Debugging Guide
PHP parse errors and syntax errors prevent the PHP compiler from tokenizing and executing your code. Discover how to read PHP parser error messages, identify why the line number in the error message often points to the line AFTER the actual mistake, and leverage modern linting tools.
How to Fix "Cannot Modify Header Information - Headers Already Sent" in PHP
The warning "Cannot modify header information - headers already sent by (output started at...)" occurs when a script attempts to send HTTP headers (header(), setcookie(), session_start()) after HTML, whitespace, or error text has already been dispatched to the browser.
How to Fix "Fatal Error: Maximum Execution Time of 30 Seconds Exceeded" in PHP
PHP enforces a maximum execution timeout (default 30 seconds) to prevent frozen scripts from exhausting server CPU threads. Learn how to diagnose infinite loops versus legitimate long-running tasks like CSV exports and backups.
How to Fix "Fatal Error: Allowed Memory Size of X Bytes Exhausted" in PHP
When a PHP script attempts to allocate more RAM than allowed by memory_limit (e.g. 128MB or 256MB), PHP halts execution. Discover how to increase memory limits cleanly and optimize unbuffered SQL queries.
How to Fix "cURL Error 60: SSL Certificate Problem: Unable to Get Local Issuer Cert"
When PHP cURL calls an external HTTPS API (Stripe, PayPal, Google, WordPress.org), it verifies the remote server's certificate. On local Windows/XAMPP environments without an active CA bundle, verification fails with error 60.
How to Fix PHP json_decode() Returning NULL: Causes and Diagnostic Solutions
When PHP's json_decode() returns NULL instead of an array or object, the input string violates the RFC 8259 JSON standard. Learn how to diagnose errors using json_last_error_msg(), handle UTF-8 BOM headers, and fix single-quote strings.
How to Fix "Warning: Undefined Array Key" in PHP 8.x: Clean Migration Guide
In PHP 8.0+, accessing an array index that does not exist was upgraded from an E_NOTICE to an E_WARNING ("Warning: Undefined array key"). Learn how to use the null coalescing operator to write clean, warning-free code.
How to Fix "Fatal Error: Class Not Found" in PHP: Composer PSR-4 Autoloading Guide
The fatal error "Class 'App\Models\User' not found" indicates the Composer autoloader or spl_autoload_register failed to locate and require the corresponding PHP file. The most common cause is a discrepancy between folder names and namespace capitalization.
How to Secure PHP File Upload Scripts: Complete Hardening & Prevention Guide
Insecure file upload forms are one of the most critical security vulnerabilities, allowing attackers to upload malicious .php webshells and take over the server. Learn how to build a defense-in-depth upload pipeline.