headers_sent — Checks if or where headers have been sent

2018-01-19 14:51:01
linefo
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最后编辑:linefo 于 2018-01-19 14:53:24

headers_sent

(PHP 4, PHP 5, PHP 7)

headers_sentChecks if or where headers have been sent

说明

bool headers_sent ([ string &$file [, int &$line ]] )

Checks if or where headers have been sent.

You can't add any more header lines using the header() function once the header block has already been sent. Using this function you can at least prevent getting HTTP header related error messages. Another option is to use Output Buffering.

参数

file

If the optional file and line parameters are set, headers_sent() will put the PHP source file name and line number where output started in the file and line variables.

line

The line number where the output started.

返回值

headers_sent() will return FALSE if no HTTP headers have already been sent or TRUE otherwise.

范例

Example #1 Examples using headers_sent()

<?php

// If no headers are sent, send one
if (!headers_sent()) {
    
header('Location: http://www.example.com/');
    exit;
}

// An example using the optional file and line parameters, as of PHP 4.3.0
// Note that $filename and $linenum are passed in for later use.
// Do not assign them values beforehand.
if (!headers_sent($filename$linenum)) {
    
header('Location: http://www.example.com/');
    exit;

// You would most likely trigger an error here.
} else {

    echo 
"Headers already sent in $filename on line $linenum\n" .
          
"Cannot redirect, for now please click this <a " .
          
"href=\"http://www.example.com\">link</a> instead\n";
    exit;
}

?>

注释

Note:

数据头只会在SAPI支持时得到处理和输出。

参见

  • ob_start() - 打开输出控制缓冲
  • trigger_error() - 产生一个用户级别的 error/warning/notice 信息
  • headers_list() - Returns a list of response headers sent (or ready to send)
  • header() - 发送原生 HTTP 头 for a more detailed discussion of the matters involved.