Example of PHP header function usage (2)

Header ("location:http://www.php.net";); Exit After each redirect, "Exit" must be added to avoid an error and continue execution. ?> Header ("refresh:3;url=http://bbs.it-home.org"); Print (' Loading, please wait ... Three seconds after the automatic jump ~ ~ ~ '); Header redirection is equivalent to entering a URL for the user in the Address bar ?> Copy Code Example two: Prohibit page in IE cache users can get the latest information every time, instead of Proxy or cache data, you can use the following headers Header (' Expires:mon, Jul 1997 05:00:00 GMT '); Header (' last-modified: '. Gmdate (' d, D M Y h:i:s '). ' GMT '); Header (' Cache-control:no-store, No-cache, Must-ridate '); Header (' cache-control:post-check=0, pre-check=0 ', false); Header (' Pragma:no-cache ');//compatible with http1.0 and HTTPS ?> Copy Code CacheControl = No-cachepragma=no-cacheexpires =-1 expires is a good thing, if the Web page on the server changes frequently, set it to 1, which means that it expires immediately. If a webpage is updated daily 1 o'clock in the morning, you can set expires to 1 o'clock in the morning the next day. When the HTTP1.1 server specifies CacheControl = No-cache, the browser does not cache the page. Legacy HTTP 1.0 Servers cannot use the Cache-control header. So for backwards compatibility with HTTP 1.0 servers, IE uses the Pragma:no-cache header to provide special support for HTTP. Internet Explorer does not cache this response if the client communicates with the server over a secure connection (https://) and the server returns a Pragma:no-cache header in the response. Note: Pragma:no-cache prevents caching only when used in a secure connection, and if used in a non-secure page, is processed in the same way as expires:-1, the page is cached but is marked for immediate expiration. HTTP-EQUIV META tag: You can use HTTP-EQUIV meta to mark the header of a specified HTTP message in an HTML page. Older versions of IE may not support HTML meta tags, so it is best to use the HTTP message header to disable caching. Example three: Let the user's browser appear unable to find the file information. PHP's function header () can send a Status header to the browser, such as the header ("status:404 not Found"). However, the response returned by the browser is actually: Header ("Content-type:application/x-gzip"); Header ("content-disposition:attachment; Filename= file name "); Header ("Content-description:php3 Generated Data"); ?> Copy Code Example five: header function input before the header function is generally not able to output HTML content, similar to the Setcookie () and session functions, these functions need to increase the message header information in the output stream. If there is an echo statement before the header () is executed, the "Warning:cannot Modify header Information–headers already sent by ..." error is reported when the header () is encountered later. This means that there cannot be any text, blank lines, carriage returns, etc. in front of these functions, and it is best to add the exit () function after the header () function. For example, in the following error notation, there is a blank line between the two PHP code snippets: Some code here ?> This is supposed to be a blank line. Header ("http/1.1 403 Forbidden"); Exit (); ?> Copy Code Cause: When the PHP script starts executing, it can send both the HTTP message header (header) information and the principal information. The HTTP message header (from the header () or the Setcookie () function) is not immediately sent, instead it is saved to a list. This allows you to modify the header information, including the default title (for example, the Content-type title). However, once the script sends any non-header output (for example, using HTML or print () calls), then PHP must first send all headers and then terminate HTTP header. Then continue to send the principal data. From this point on, any attempt to add or modify header information is not allowed, and one of the above error messages is sent. Workaround: Modify php.ini to open the cache (output_buffering), or use the cache function Ob_start (), Ob_end_flush (), etc. in the program. The principle is: When output_buffering is enabled, PHP does not send an HTTP header when the script sends the output. Instead, it imports this output through a pipeline (pipe) into a dynamically increasing cache (only used in PHP 4.0, which has a centralized output mechanism). You can still modify/add a header, or set a cookie because the header is not actually sent. When all the scripts are terminated, PHP automatically sends the HTTP header to the browser, and then sends the contents of the output buffer.

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