IE下COOKIE失效的一种特殊情况
setcookie ("name", "value", 0, "/", ".example.com");
使用以上代码设置cookie后，在非IE（chrome、firefox等）下访问 test_1.example.com 均可正常获取；使用IE访问则获取不到该cookie。
访问 test.example.com 任何浏览器均可正常获取。
本来以为是setcookie参数问题，后来以为是两套代码不同问题，发现都不是。
最后发现是域名问题：域名中不能含有“_”（下划线）。。。
------------------------------我是分割线-------------------------------
RFC 952 有明文规定
A "name" (Net, Host, Gateway, or Domain name) is a text string up to 24 characters drawn from the alphabet (A-Z), digits (0-9), minus sign (-), and period (.) . Note that periods are only allowed when they serve to delimit components of "domain style names". (See RFC-921, "Domain Name System Implementation Schedule", for background). No blank or space characters are permitted as part of a name. No distinction is made between upper and lower case. The first character must be an alpha character. The last character must not be a minus sign or period. A host which serves as a GATEWAY should have "-GATEWAY" or "-GW" as part of its name. Hosts which do not serve as Internet gateways should not use "-GATEWAY" and "-GW" as part of their names. A host which is a TAC should have "-TAC" as the last part of its host name, if it is a DoD host. Single character names or nicknames are not allowed.
虽然很多网站，甚至是某些知名网站的一些二级域名仍有采用这种不规范命名，但大家在平时使用中还是最好应尽量避免使用带有下划线的域名。