问题
My code is simple:
<!DOCTYPE html>
<html>
<head>
...
<?php var_dump(headers_sent()); ?>
It returns false. Shouldn't the headers be sent immediately after something is printed? Like just after the first < character.
回答1:
It depends if your output_buffering directive in php.ini file. If it is Off
output_buffering = Off
then echo headers_sent() should output 1
In other cases, headers_sent() won't output any results because it will be FALSE. The headers won't be sent because the output is buffered.
If you want to get around this and force-send headers, you can use flush().
Hope this helps!
回答2:
Read the comments in docs!
Here, for example: http://es1.php.net/manual/en/function.headers-sent.php#75835
He do a great exposition :P
Edit
Yes, headers_sent() will return false, even if you sent something to the ouptut using print() or header() , if output_buffering is different from Off in you php.ini, and the length of what you sent does not exceed the size of output_buffering. [...] This is noticed in php.ini comment : "Output buffering allows you to send header lines (including cookies) even after you send body content, in the price of slowing PHP's output layer a bit."
回答3:
I managed to find a way without deactivating the output_buffering :
if (!headers_sent() && !ob_get_contents()) {
// do your thing
}
来源：https://stackoverflow.com/questions/17588563/headers-sent-return-false-but-headers-were-sent