PHP Error Handling Logging Errors

PHP Error Handling

Logging Errors

Problem

You want to save program errors to a log. These errors can include everything from parser errors and files not being found to bad database queries and dropped connections.

Solution

Use error_log() to write to the error log:

       // LDAP error

       if (ldap_errno($ldap)) {

            error_log("LDAP Error #" . ldap_errno($ldap) . ": " . ldap_error($ldap));

       }

Discussion

Logging errors facilitates debugging. Smart error logging makes it easier to fix bugs. Always log information about what caused the error:

       $r = mysql_query($sql);

       if (! $r) {

            $error = mysql_error();

            error_log('[DB: query @'.$_SERVER['REQUEST_URI']."][$sql]: $error");

       } else {

            // process results

       }

You’re not getting all the debugging help you could be if you simply log that an error occurred without any supporting information:

       $r = mysql_query($sql);

       if (! $r) {

            error_log("bad query");

       } else {

            // process result

       }

Another useful technique is to include the __FILE__, __LINE__, __FUNCTION__, __CLASS__, and __METHOD__ “magic” constants in your error messages:

       error_log('['.__FILE__.']['.__LINE__."]: $error");

The __FILE__ constant is the current filename, __LINE__ is the current line number, __FUNCTION__ is the current function name, __METHOD__ is the current method name (if any), and __CLASS__ is the current class name (if any). Starting with PHP 5.3.0, __DIR__ is the directory that __FILE__ is in and __NAMESPACE__ is the current namespace. Starting in PHP 5.4.0, __TRAIT__ is the current trait name (if any).