预定义常量
下列常量作为 PHP 核心的一部分总是可用的。
- 
    PHP_OUTPUT_HANDLER_START(integer)
- 
    Indicates that output buffering has begun. 
- 
    PHP_OUTPUT_HANDLER_WRITE(integer)
- 
    Indicates that the output buffer is being flushed, and had data to output. Available since PHP 5.4. 
- 
    PHP_OUTPUT_HANDLER_FLUSH(integer)
- 
    Indicates that the buffer has been flushed. Available since PHP 5.4. 
- 
    PHP_OUTPUT_HANDLER_CLEAN(integer)
- 
    Indicates that the output buffer has been cleaned. Available since PHP 5.4. 
- 
    PHP_OUTPUT_HANDLER_FINAL(integer)
- 
    Indicates that this is the final output buffering operation. Available since PHP 5.4. 
- 
    PHP_OUTPUT_HANDLER_CONT(integer)
- 
    Indicates that the buffer has been flushed, but output buffering will continue. As of PHP 5.4, this is an alias for PHP_OUTPUT_HANDLER_WRITE.
- 
    PHP_OUTPUT_HANDLER_END(integer)
- 
    Indicates that output buffering has ended. As of PHP 5.4, this is an alias for PHP_OUTPUT_HANDLER_FINAL.
- 
    PHP_OUTPUT_HANDLER_CLEANABLE(integer)
- 
    Controls whether an output buffer created by ob_start() can be cleaned. Available since PHP 5.4. 
- 
    PHP_OUTPUT_HANDLER_FLUSHABLE(integer)
- 
    Controls whether an output buffer created by ob_start() can be flushed. Available since PHP 5.4. 
- 
    PHP_OUTPUT_HANDLER_REMOVABLE(integer)
- 
    Controls whether an output buffer created by ob_start() can be removed before the end of the script. Available since PHP 5.4. 
- 
    PHP_OUTPUT_HANDLER_STDFLAGS(integer)
- 
    The default set of output buffer flags; currently equivalent to PHP_OUTPUT_HANDLER_CLEANABLE|PHP_OUTPUT_HANDLER_FLUSHABLE|PHP_OUTPUT_HANDLER_REMOVABLE.Available since PHP 5.4.