‘sync’ was not declared in this scope

Asked Jun 11 '20 at 11:35

Active Jun 11 '20 at 11:35

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I want to clear cache during an ongoing script before I benchmark some results, and I use the answer mentioned in this question for that.

The answer basically is:

sync();

std::ofstream ofs("/proc/sys/vm/drop_caches");
ofs << "3" << std::endl;

But when I do that, I get:

rTree.cpp:157:4: error: ‘sync’ was not declared in this scope
  157 |    sync();
      |    ^~~~

I tried to google, but almost every link is related to variables/methods not being declared in the scope (I can see why, but that doesn't really solve my problem). Any would be great, thanks...

asked Jun 11 '20 at 11:35

Ankit Kumar

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what is `sync` ? Don't blindy copy others code without knowing what it is (not even fro SO ;). Did you include the necessary header? – 463035818_is_not_an_ai Jun 11 '20 at 11:44
@idclev463035818 Yup, `` – Ankit Kumar Jun 11 '20 at 11:47
I somewhat suspect it's the POSIX call to sync memory buffers to on-disk commit. [see here](https://linux.die.net/man/3/sync). You included `unistd.h`, *right* ? – WhozCraig Jun 11 '20 at 11:48
if it was from `istream` it would be `std::sync`, but it isnt – 463035818_is_not_an_ai Jun 11 '20 at 11:49
@WhozCraig it works (compiles)! It should work on runtime too. Thanks :) – Ankit Kumar Jun 11 '20 at 11:49
@idclev463035818 I didn't know (at all) it's from that header. So... – Ankit Kumar Jun 11 '20 at 11:51
@idclev463035818 Ah yes, I did that after the link was posted :) – Ankit Kumar Jun 11 '20 at 11:54

‘sync’ was not declared in this scope

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