char url[128];
sprintf(url,"http://passport.csdn.net/ajax/accounthandler.ashx?t=log&u=%s&p=%s&remember=0&f=http%3A%2F%2Fwww.csdn.net%2F&rand=0.47590136872096434",strUser,strPass);

这个URL长度肯定不止128……