PHP 5.5，如何启用odbc_connect（）？

Question

I'm using PHP 5.5.6 on Redhat6.

When I run the following PHP scrip I get a Call to undefined function odbc_connect()error.

$u = 'smthg';
$p = 'smthgelse';

$conn = odbc_connect('MSSQL-PHP', $u, $p , SQL_CUR_USE_DRIVER) ;

I configured my odbc.ini file as following:

[MSSQL-PHP]
Driver                  = SQL Server Native Client 11.0
Server                  = 10.33.37.2
Database                = MyDBName

I also try to connect to my server with PDO but I also get a Class 'PDO' not found error.

I thought that both ODBC and PDO extension was already included in PHP5.5, and there was no extension to add into my php.ini file. But a php -r 'phpinfo();' | grep odbc or the same with pdo give me nothing.

What did I miss?