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php setcookie reports an error because setcookie() has output before. The solution is to send the output echo data and the cookie in the header together.
The operating environment of this article: windows7 system, PHP7.1 version, DELL G3 computer
What should I do if php setcookie reports an error?
There cannot be any output before PHP setcookie()
PHP’s setcookie function, the manual says this:
setcookie() defines a cookie to be sent along with the rest of the HTTP headers. Like other headers, cookies must be sent before any output from your script (this is a protocol restriction). This requires that you place calls to this function prior to any output, including <html> and <head> tags as well as any whitespace.
The general meaning is Nothing can be output to the client browser before setcookie, otherwise an error will be reported. However, after testing, it was found that no error was reported. Continue to read the manual:
You can use output buffering to send output prior to the call of this function, with the overhead of all of your output to the browser being buffered in the server until you send it. You can do this by calling ob_start() and ob_end_flush() in your script, or setting the output_buffering configuration directive on in your php.ini or server configuration files.
So I modified the output_buffering of php.ini (PHP version 5.4) to 0, which means turning off the buffer. (It is closed below PHP 5.3, and is enabled by default after 5.3, with a value of 4096)
means that if ob_start and ob_end_flush are set to output the buffer before outputting the cookie, no error will be reported. So, why is there no error when the cookie and buffer data are returned together? It should be because: the data in the buffer will be organized into a complete HTTP packet and sent out.
We can take a look at the error message:
echo "i am going to setcookie"; var_dump(setcookie('buhehe', 'asdasdasdasdad')); print_r($_COOKIE);
"Please do not modify the header information because the header has already been sent." Obviously, buffering is not used area output, the header will be returned to the browser first, and then when setcookie is used to send the header information, an error will be reported - it does not comply with the specifications of the HTTP protocol. Because the HTTP protocol stipulates that the header should be output before the body.
I modified the code and sent the output echo data and the cookie in the header together.
ob_start(); echo "i am going to setcookie"; var_dump(setcookie('buhehe', 'asdasdasdasdad')); ob_end_flush(); print_r($_COOKIE);
The results are as follows:
When you set output_buffering to 0, that is, when you turn off the buffer in php.ini, you need to manually ob_start to turn on the buffer. District.
Why do some developers, when testing, find that there is no error after echoing the information before setcookie?
Because most of the current PHP applications are 5.3, and some even use 7. In the PHP5.3 version, because the buffer is enabled by default and the default size is 4096, the echo data before setcookie and the cookie header information will be encapsulated into an HTTP packet in the buffer and sent to the client~ Therefore, the error message in the picture above will not be generated (please do not modify the HTTP header information)~~
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