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What Output Is Buffered?
PHP's user-level output buffers buffer all output after they are started
until they are turned off or the script ends.
Output in the context of PHP's user-level output buffer
is everything that PHP would display or send back to the browser.
In practical terms, output is non-zero length data that is:
-
outside of the
<?php ?> tags
-
printed by language constructs and functions
whose explicit purpose is to output user provided variables or strings such as
echo, print,
printf, var_dump,
var_export, vprintf
-
printed by functions whose purpose is to collect and output
data/information on the running script or PHP such as
debug_print_backtrace, phpcredits,
phpinfo,
ReflectionExtension::info
-
printed by PHP on an uncaught exception or an unhandled error
(subject to the settings of
display_errors
and error_reporting)
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anything written to
php://output
Note:
Data that is written directly to stdout
or passed to an SAPI function with a similar functionality
will not be captured by user-level output buffers.
This includes
writing data to stdout with fwrite
or sending headers using header
or setcookie.
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