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[std] clarify ffi C string nul term & length discussion #56140

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[std] clarify ffi C string nul term & length discussion #56140

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jnqnfe
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@jnqnfe jnqnfe commented Nov 21, 2018

re-written the paragraph, including:

  • Changed use of "calculated" to "measured". "calculated" just sounds
    wrong, giving a false impression of what strlen() does.
  • Changed "C code must manually call a function". Firstly, "manually"?
    Secondly, a function is called in Rust also... the difference is in
    what the function does - measurement v.s. reading an attribute...
  • Finished that sentence in actually stating the operation that is done.
  • Changed use of "buffer length" to "string length". Use of the term
    "buffer" here was bound to confuse.

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Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @TimNN (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Nov 21, 2018
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TimNN commented Nov 27, 2018

  • Changed use of "calculated" to "measured". "calculated" just sounds
    wrong, giving a false impression of what strlen() does.

I don't agree with the change to measured. My intuition (as a non-native English speaker) is that "measure" implies measuring something physical (e.g. distance, time). The dictionary seems to confirm that intuition.

which scans through the bytes of the string looking for the nul character marking the end, keeping a count of characters as it does so.

I don't think describing how strlen may-or-may-not be implemented internally is appropriate here. I'd rather focus on what it returns (essentially the position of the first 0 byte).

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jnqnfe commented Nov 28, 2018

I've rewritten it again, hopefully you'll like v2 better. Sorry for the delay, I've got very irregular internet access currently.

I don't agree with the change to measured. My intuition (as a non-native English speaker) is that "measure" implies measuring something physical (e.g. distance, time). The dictionary seems to confirm that intuition.

Ok, I wasn't 100% happy with it either, but it was better. I've used "counting" instead in v2.

I don't think describing how strlen may-or-may-not be implemented internally is appropriate here. I'd rather focus on what it returns (essentially the position of the first 0 byte).

I think the discussion necessitates brief mention that it involves counting. I hope you like the revised text more.

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bors commented Dec 8, 2018

☔ The latest upstream changes (presumably #56578) made this pull request unmergeable. Please resolve the merge conflicts.

@jnqnfe
clarify ffi C string nul term & length discussion
85c6548 
re-written the paragraph, including:
 - Changed use of "calculated" to "count". "calculated" just sounds
   wrong, giving a false impression of what strlen() does.
 - Changed "C code must manually call a function". Firstly, "manually"?
   Secondly, a function is called in Rust also... the difference is in
   what the function does - counting v.s. reading an attribute...
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ping from triage @TimNN awaiting your review on this

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TimNN commented Jan 15, 2019

I'm not quite sure about this PR. Some parts are certainly improved, I think, but I'm not sure about other parts of the docs here.

cc @rust-lang/docs: I would appreciated your input here.

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I preferred the original version. :-/

@Dylan-DPC-zz Dylan-DPC-zz added S-waiting-on-team Status: Awaiting decision from the relevant subteam (see the T-<team> label). and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Feb 11, 2019
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Centril commented Mar 30, 2019

cc @rust-lang/docs

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Centril commented May 29, 2019

r? @steveklabnik

@rust-highfive rust-highfive assigned steveklabnik and unassigned TimNN May 29, 2019
QuietMisdreavus
QuietMisdreavus reviewed Jun 10, 2019
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While we're in this section, i kind of want to either capitalize the use of NUL or write it as the word "null" - otherwise, to me it just looks like someone kept misspelling "null".

src/libstd/ffi/mod.rs
//! length is stored); in C it is an O(length) operation because the
//! length needs to be computed by scanning the string for the nul
//! terminator.
//! end. The length of the string is not stored, but has to be determined
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I feel like "calculated" is still a better word here? "Determined" feels like it implies that there's some kind of conceptual decision-making going on, but "calculated" feels more like it's a rote procedure that needs to be run through to figure out the length. I could be reading way too far into this, though. >_>

src/libstd/ffi/mod.rs
//! nul that marks its end, counting as it goes. The value returned by
//! common functions that perform this, is effectively the index position
//! of the nul, and thus the string length (in terms of buffer size) is
//! actually len+1. Rust strings don't have a nul terminator, their
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Part of me wants to add some types to single out what "Rust strings" actually means. Something like:

Rust strings (like &str and String) don't have a nul terminator...

On the other hand, there are many more "string" types in Rust, and e.g. OsString also stores its length separately instead of having a null byte to mark the end. Would it be too confusing to single out these types and leave out the others?

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I'm going to close this PR as it's been idle for quite a while. If you have some time to address the review comments then we'd be happy to either reopen this PR or see a new PR from you in the future. Thanks!

@apiraino apiraino removed the S-waiting-on-team Status: Awaiting decision from the relevant subteam (see the T-<team> label). label May 25, 2023
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