转自鸟哥的博客： http://www.laruence.com/2007/12/16/308.html
PHP header()
the function declaration: void header ( string string [, bool replace [, int http_response_code]])
The optional replace parameter indicates whether the header should replace a previous similar header, or add a second header of the same type. By default it will replace(true);
RFC2616有相关的所有的状态信息的说明, 就状态码，大体总结如下：
* 1xx: Informational – Request received, continuing process
* 2xx: Success – The action was successfully received, understood,
and accepted
* 3xx: Redirection – Further action must be taken in order to
complete the request
* 4xx: Client Error – The request contains bad syntax or cannot be
fulfilled
* 5xx: Server Error – The server failed to fulfill an apparently
valid request
| “100″ ; Continue
| “101″ ; Switching Protocols
| “200″ ; OK
| “201″ ; Created
| “202″ ; Accepted
| “203″ ; Non-Authoritative Information
| “204″ ; No Content
| “205″ ; Reset Content
| “206″ ; Partial Content
| “300″ ; Multiple Choices
| “301″ ; Moved Permanently
| “302″ ; Moved Temporarily
| “303″ ; See Other
| “304″ ; Not Modified
| “305″ ; Use Proxy
| “400″ ; Bad Request
| “401″ ; Unauthorized
| “402″ ; Payment Required
| “403″ ; Forbidden
| “404″ ; Not Found
| “405″ ; Method Not Allowed
| “406″ ; Not Acceptable
| “407″ ; Proxy Authentication Required
| “408″ ; Request Time-out
| “409″ ; Conflict
| “410″ ; Gone
| “411″ ; Length Required
| “412″ ; Precondition Failed
| “413″ ; Request Entity Too Large
| “414″ ; Request-URI Too Large
| “415″ ; Unsupported Media Type
| “500″ ; Internal Server Error
| “501″ ; Not Implemented
| “502″ ; Bad Gateway
| “503″ ; Service Unavailable
| “504″ ; Gateway Time-out
| “505″ ; HTTP Version not supported
So， 举几个例子：
header(“HTTP/1.1 404 Not Found”, true, 404); header(“HTTP/1.0 401 Unauthorized”); header(“Content-Type: text/html; charset=utf-8;”);
header(“Location:http://www.xxx.com”);
RFC2616 http://www.faqs.org/rfcs/rfc2616