PHP output buffering throwing warnings

Question

I have to output results while PHP script is running:

ob_implicit_flush(true);
ob_start();
for ($i=0; $i<5; $i++) {
    echo $i . ' - ';
    ob_end_flush();
    flush();
    sleep(1);
}

This is working but throwing warnings:

Notice: ob_end_flush(): failed to delete and flush buffer. No buffer to delete or flush in ...

How to fix that?

Think again and choose another way. – u_mulder Aug 09 '18 at 11:56 — u_mulder, Aug 09 '18 at 11:56
You should only call `ob_end_flush()` once at the end. – Blue Aug 09 '18 at 11:59 — Blue, Aug 09 '18 at 11:59

Jim Wright · Answer 1 · 2018-08-09T12:00:54.027

2

In the first loop you are ending the buffer. If you want to do that, you should start a new buffer in each loop.

ob_implicit_flush(true);
for ($i=0; $i<5; $i++) {
    ob_start();
    echo $i . ' - ';
    ob_end_flush();
    flush();
    sleep(1);
}

This is a neater way to use buffering. It is also more performant as you are only using 1 buffer. If you do not need to flush on each loop, you could skip the ob_flush within the loop and use ob_end_flush instead of ob_end_clean.

ob_implicit_flush(true);
ob_start();
for ($i=0; $i<5; $i++) {
    echo $i . ' - ';
    ob_flush();
    flush();
    sleep(1);
}
ob_end_clean();

edited Aug 09 '18 at 12:00

answered Aug 09 '18 at 11:56

Jim Wright

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Thanks! but if starting a new buffer in each loop will have impact on performance, would it be better to just clean the first and re-use it? and how to do it? – medk Aug 09 '18 at 11:59
1

Why start the buffer multiple times? All he needs is `ob_flush()` – Blue Aug 09 '18 at 12:00
@FrankerZ I was editing the answer as you wrote your comment :P – Jim Wright Aug 09 '18 at 12:01
@JimWright this method is not working as it echoes everything at once and not after each loop – medk Aug 09 '18 at 12:05
3

@medk Have a look [here](https://stackoverflow.com/questions/6001628/php-flush-not-working-in-chrome). Output buffering can be a bit finicky in browsers. – Blue Aug 09 '18 at 12:08

Blue · Answer 2 · 2018-08-09T12:03:44.983

1

ob_end_flush() will disable buffering, so future calls to this in your loop will fail. Simply use ob_flush(), which clears the buffer but maintains output buffering:

ob_implicit_flush(true);
ob_start();
for ($i=0; $i<5; $i++) {
    echo $i . ' - ';
    ob_flush();
    sleep(1);
}
ob_end_flush();

edited Aug 09 '18 at 12:03

answered Aug 09 '18 at 12:02

Blue

22,608
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You don't need to flush after the loop. – Jim Wright Aug 09 '18 at 12:03
If he had additional code afterwards, or anything else he is going to echo (Such as a final end statement.) It's important to include. – Blue Aug 09 '18 at 12:04

score 0 · Answer 3 · answered Aug 09 '18 at 14:28

0

Ok, I fixed it like that:

ob_implicit_flush(true);
ob_start();
for ($i=0; $i<5; $i++) {
    echo $i . ' - ';
    flush();
    @ob_flush();
    @ob_end_clean();
    sleep(1);
}

It works now.

answered Aug 09 '18 at 14:28

medk

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PHP output buffering throwing warnings

3 Answers3