Php_mysqli.dll problems

Run a code for the php_mysqli.dll problem, and Fatalerror: fatal: runtime. phponline104 occurs. Then I remove the semicolon in front of extensionphp_mysqli.dll, restart apache, and then all php cannot run. the php_mysqli.dll problem
Run a code with Fatal error: Class 'mysqli' not found in C: \ temp \ PhPWeb \ microblog \ dao \ UserDao. php on line 104

Then I remove the semicolon before extension = php_mysqli.dll, restart apache, and then all php cannot be run. then I can run the semicolon before it is added to solve the problem.

------ Solution --------------------
Check whether the php_mysqli.dll file exists in the extension directory...

------ Solution --------------------
Run phpinfo () to view the running database
------ Solution --------------------
Configure extension_dir = "php installation directory/ext ";