Fatal error: Call to undefined function sqlsrv_select_db() in C:AppServwwwSKNINCincludedb_connect.php on line 17

<?php
$serverName = "serverName\instanceName";
$connectionInfo = array( "Database"=>"dbName", "UID"=>"username", "PWD"=>"password");
$conn = sqlsrv_connect( $serverName, $connectionInfo );
if( $conn === false ) {
    die( print_r( sqlsrv_errors(), true));
}

$sql = "SELECT FirstName, LastName FROM SomeTable";
$stmt = sqlsrv_query( $conn, $sql );
if( $stmt === false) {
    die( print_r( sqlsrv_errors(), true) );
}

while( $row = sqlsrv_fetch_array( $stmt, SQLSRV_FETCH_ASSOC) ) {
      echo $row['LastName'].", ".$row['FirstName']."<br />";
}

sqlsrv_free_stmt( $stmt);
?>