TP3 Undefined class constant ' Mysql_attr_init_c.

Phpinfo (); There is a configuration file (php.ini) and a loaded configuration file whose precedence is higher than the former! If the latter is null, the former will prevail; this is the Apache read php.ini location, not read the PHP installation directory. Loaded Configuration File This value can be modified by httpd.conf's Phpinidir parameter

Thinkphp3.2, in common, the config.php configuration of the constant connection to MySQL
But show:
Undefined class constant ' Mysql_attr_init_command

This is mostly due to the failure to connect the php_pdo_mysql.dll extension of ext in the PHP directory

Httpd.conf in Apache can read the location of php.ini

But the php.ini load extension is easy to overlook, and the No. 734 line in php5.6 PHP.ini has
The directory under Windows extension, remove the semicolon, and then write the location of ext extension
Notice what is in the path? Of

TP3 Undefined class constant ' Mysql_attr_init_c.