php7.1.5提示Call to undefined function sqlsrv_connect()

我安装环境是WindowsServer2012X64+sqlserver2012+IIS8+PHP7.1.5
已经下载了php_sqlsrv_7_nts_x64.dll和php_pdo_sqlsrv_7_nts_x64.dll
在运行测试程序的时候提示：
PHP Fatal error: Uncaught Error: Call to undefined function sqlsrv_connect() in C:\inetpub\wwwroot\gbm\xxjsb\b.php:5 Stack trace: #0 {main} thrown in C:\inetpub\wwwroot\gbm\xxjsb\b.php on line 5 
 
<?php
$serverName = "16.49.32.108"; //serverName\instanceName
$connectionInfo = array("cardb","sa","qhdsql");
//$connectionInfo = array( "Database"=>"cardb", "UID"=>"sa", "PWD"=>"qhdsql");
$conn = sqlsrv_connect($serverName,$connectionInfo);
//$conn = mssql_connect('16.49.32.108','sa','qhdsql');
//$conn = odbc_connect('108','sa','qhdsql');//if( $conn ) {
     echo "Connection established.<br />";
//}else{
     echo "Connection could not be established.<br />";
//     die( print_r( sqlsrv_errors(), true));
//}
?>