在照彭武兴先生的《php bible》中所述，header可以送出status标头，如
<?php
header("status: 404 not found");
?>
就可以让用户浏览器出现文件找不到的404错误，但是我试了这样是不行的。
后来我到w3.org上查了http的相关资料，终于试出来了如何header出状态代码(status)，与大家分享。
其实应该是这样的:
header("http/1.1 403 forbidden");
?>
第一部分为http协议的版本(http-version)
第二部分为状态代码(status)
第三部分为原因短语(reason-phrase)
三部分中间用一个空格分开，且中间不能有回车,第一部分和第二部分是必需的，第三部分则是给人看的，可写可不写甚至乱写。
还有，这一句的输出必须在html文件的第一行。
下面我给出各代码所代表的意思(是从w3.org上查到的,够权威了):
* 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
