ob_get_flush flushes the output buffer, return it as a string and turns off output buffering.
The output buffer must be started by ob_start with PHP_OUTPUT_HANDLER_FLUSHABLE flag. Otherwise ob_get_flush will not work.
This function is similar to ob_end_flush, except that this function also returns the buffer as a string.
This function has no parameters.
Returns the output buffer or false if no buffering is active.