whats the difference between ob_flush and ob_end_flush?

Question

i am confused about the PHP functions ob_flush() and ob_end_flush(). About the function ob_flush the manual says

The buffer contents are discarded after ob_flush() is called.This function does not destroy the output buffer like ob_end_flush() does. 

i am confused about the words discarded and destroyed here. Even if the buffer contents are discarded in case of ob_flush() they cant be accessed and even if they are destroyed as in case of ob_end_flush() they cant be accessed. Then whats the difference between these two functions?

UPDATE:

In response to JamWaffles answer I dont understand the significance of deleting everything in the buffer but keeping the buffer vs deleting the whole buffer(freeing it) because PHP has no concept of pointers and you cant get the address of buffers so it should be immaterial whether you keep the empty buffer with you or you free it

Answer 1

I think in this case they mean the same thing. ob_flush() is used when you want to flush parts of the page to the client, whereas ob_end_flush() flushes the entire buffer, then destroys the buffer. What ob_flush() does is delete everything in the buffer, but keeps the buffer itself so more data can be put into it after the ob_flush() call.

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I'll try to explain better.

Discarded

Let's say I have a nice, bright orange plastic bucket. This is my buffer. I then get some sand, representing the contents of the buffer, and fill the buffer (bucket) up. I then pick this bucket with sand in it up and pour it into a sandpit, which is my client. You'll notice the sand is gone, yet the bucket remains. This is what is meant by the buffer contents are discarded - the buffer itself can be re-used (filled up with sand again). In memory terms, the memory is emptied but not freed, so it can be filled again.

Destroyed

Now, if we take our bucket again, fill it up with sand once more, empty the sand out and then set fire to the bucket because we don't require it any longer, that's called destroying the buffer; the data in the buffer is gone, but so is the buffer itself. In memory terms, the memory is freed for other use.

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Is this significant in PHP, without pointers, the OP asks? Well, it depends what you want to do. If you're processing a long page, and want to (for example) send the header and sidebar to the client while you process the rest of the page for sending after it's done, use ob_flush().

If you want to flush something to the client without any more output after it, use ob_end_flush().

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I mean absolutely no disrespect in talking in a rather patronising tone; I wanted to make an analogy to make the definitions as clear as possible.