var xmlHttp;
//建立对象
function createXMLHttpRequest()
{
	if(window.ActiveXObject)
	{
		xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
	}
	else if(window.XMLHttpRequest)
	{
		xmlHttp=new XMLHttpRequest();
	}
}
function makeRandChar(chars,marklen)
{
    var tmpstr = '';
    var chrlen = chars.length;
    var iRandom ;
    do{
        iRandom = Math.round(Math.random() * chrlen);
        tmpstr += chars.charAt(iRandom);
        if( tmpstr.length == marklen ) break;    
    }
    while (tmpstr.length < marklen)
    return tmpstr;
}