SL.io.50 (Avoid `endl`): Mention string streams #1920

N-Dekker · 2022-06-02T19:47:12Z

Explicitly mentioned string streams as endl insertions into string streams do actually occur in the wild.

People have been wondering whether endl is specifically useful for a stringstream to get a platform-specific end-of-line character sequence (apparently not):
"Inserting endline into a stringstream"
https://stackoverflow.com/questions/6865398/inserting-endline-into-a-stringstream

But there have also been concerns about the performance effect of endl on an ostringstream:
"Why does using std::endl with ostringstream affect output speed?"
https://stackoverflow.com/questions/12675273/why-does-using-stdendl-with-ostringstream-affect-output-speed

cubbimew · 2022-06-06T02:06:56Z

CI wants ostringstream to be added to scripts/hunspell/isocpp.dic

And yes, I've also seen the "platform-specific end-of-line" urban legend, I wonder if it should be called out explicitly.

Explicitly mentioned string streams as `endl` insertions into string streams do actually occur in the wild. With help from Sergey Zubkov.

N-Dekker · 2022-06-06T09:58:05Z

@cubbimew Thanks for your comments. Can you please check if I addressed them correctly and sufficiently?

BenjamenMeyer · 2022-06-06T15:25:29Z

CppCoreGuidelines.md

+to the insertion of a `'\n'` character, but also in this case, `endl` might be significantly slower.
+
+`endl` does *not* take care of producing a platform specific end-of-line sequence (like "\r\n" on
+Windows). So for a string stream, `s << endl` just inserts a *single* character, `'\n'`.


or \n\r for Mac ;)

or \n\r for Mac ;)

@BenjamenMeyer You mean '\r', right? But hasn't Mac moved towards using just a single \n, nowadays? Otherwise, are there still actively used C++11 Standard Library implementations for Mac whose file output streams produce a '\r' on each end-of-line?

I did notice the smiley in your comment, but I just want to be entirely sure that it's OK not to mention the old Mac '\r' in the proposed text.

@N-Dekker AFAIK mac is still doing the \n\r - now, perhaps it changes from application to application, but I've still seen it in recent years. The new text called out the Windows behavior as an example; it could be worth noting (legacy or otherwise) the Mac behavior too.

I just want to be entirely sure that it's OK not to mention the old Mac '\r' in the proposed text.

Please don't mention Macs. Your proposed change is fine. What matters is that it doesn't output a platform-specific line ending, you don't need to give multiple examples of things it doesn't do.

I'm fine with this PR documenting it ;) (e.g not a change - just the commentary here)

@jwakely @BenjamenMeyer Thanks, I won't mention old Macs line endings, if it isn't really necessary. So I also think the PR is OK now.

BenjamenMeyer · 2022-06-06T15:26:44Z

cool - glad to have this documented. too bad we can't link back to the definition of std::endl for more authority; but this should do just fine and help curb those urban legends.

jleffler · 2022-06-07T17:48:06Z

On a Mac running modern macOS (MacOS X or later; anything currently supported by Apple), the default line ending is Unix-style \n line endings. AFAIK, the older Macs (20+ years old now) and MacOS 9 or earlier used \r (only; not either \r\n or \n\r) for the line endings.

…

On Tue, Jun 7, 2022 at 9:56 AM Benjamen Meyer ***@***.***> wrote: ***@***.**** commented on this pull request. ------------------------------ In CppCoreGuidelines.md <#1920 (comment)> : > @@ -20308,6 +20308,14 @@ For writing to a file, there is rarely a need to `flush`. ##### Note +For string streams (specifically `ostringstream`), the insertion of an `endl` is entirely equivalent +to the insertion of a `'\n'` character, but also in this case, `endl` might be significantly slower. + +`endl` does *not* take care of producing a platform specific end-of-line sequence (like "\r\n" on +Windows). So for a string stream, `s << endl` just inserts a *single* character, `'\n'`. @N-Dekker <https://github.com/N-Dekker> AFAIK mac is still doing the \n\r - now, perhaps it changes from application to application, but I've still seen it in recent years. The new text called out the Windows behavior as an example; it could be worth noting (legacy or otherwise) the Mac behavior too. — Reply to this email directly, view it on GitHub <#1920 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ACCAHBXD2POYTHTRCU7RZWTVN5WLNANCNFSM5XWA6X7Q> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

-- Jonathan Leffler ***@***.***> #include <disclaimer.h> Guardian of DBD::Informix - v2018.1031 - http://dbi.perl.org "Blessed are we who can laugh at ourselves, for we shall never cease to be amused."

hsutter · 2022-06-13T16:12:03Z

Editors call: Great, thanks!

* F.16 ("in" parameters): Move Matrix example to F.20 (return values) (isocpp#1922) The `Matrix` example and the notes about assignment appear off-topic in rule F.16, as F.16 is specifically about "in" parameters. With help from Sergey Zubkov. * SL.io.50 (Avoid `endl`): Mention string streams (isocpp#1920) Explicitly mentioned string streams as `endl` insertions into string streams do actually occur in the wild. With help from Sergey Zubkov. * Extended E.16 to include copy ctor for exception type, closes isocpp#1921 * Fix GitHub Actions build warnings, Marker style should be `*` (isocpp#1925) * restored reference * Added references to note Co-authored-by: Niels Dekker <[email protected]> Co-authored-by: Herb Sutter <[email protected]>

* F.16 ("in" parameters): Move Matrix example to F.20 (return values) (isocpp#1922) The `Matrix` example and the notes about assignment appear off-topic in rule F.16, as F.16 is specifically about "in" parameters. With help from Sergey Zubkov. * SL.io.50 (Avoid `endl`): Mention string streams (isocpp#1920) Explicitly mentioned string streams as `endl` insertions into string streams do actually occur in the wild. With help from Sergey Zubkov. * Extended E.16 to include copy ctor for exception type, closes isocpp#1921 * Fix GitHub Actions build warnings, Marker style should be `*` (isocpp#1925) * C.166: Use markdown format and document title for link (isocpp#1929) * C.9: Improve an inline link (isocpp#1933) Avoid ending the sentence with a dangling "see". Co-authored-by: Niels Dekker <[email protected]> Co-authored-by: Herb Sutter <[email protected]> Co-authored-by: Francisco Moretti <[email protected]> Co-authored-by: Sven van Haastregt <[email protected]>

* Update CppCoreGuidelines.md * Update CppCoreGuidelines.md * Update isocpp.dic * use snake casing * sake case naming * C 32 comments (#3) * F.16 ("in" parameters): Move Matrix example to F.20 (return values) (isocpp#1922) The `Matrix` example and the notes about assignment appear off-topic in rule F.16, as F.16 is specifically about "in" parameters. With help from Sergey Zubkov. * SL.io.50 (Avoid `endl`): Mention string streams (isocpp#1920) Explicitly mentioned string streams as `endl` insertions into string streams do actually occur in the wild. With help from Sergey Zubkov. * Extended E.16 to include copy ctor for exception type, closes isocpp#1921 * Fix GitHub Actions build warnings, Marker style should be `*` (isocpp#1925) * restored reference * Added references to note Co-authored-by: Niels Dekker <[email protected]> Co-authored-by: Herb Sutter <[email protected]> Co-authored-by: Niels Dekker <[email protected]> Co-authored-by: Herb Sutter <[email protected]>

* F.16 ("in" parameters): Move Matrix example to F.20 (return values) (isocpp#1922) The `Matrix` example and the notes about assignment appear off-topic in rule F.16, as F.16 is specifically about "in" parameters. With help from Sergey Zubkov. * SL.io.50 (Avoid `endl`): Mention string streams (isocpp#1920) Explicitly mentioned string streams as `endl` insertions into string streams do actually occur in the wild. With help from Sergey Zubkov. * Extended E.16 to include copy ctor for exception type, closes isocpp#1921 * Fix GitHub Actions build warnings, Marker style should be `*` (isocpp#1925) * C.166: Use markdown format and document title for link (isocpp#1929) * C.9: Improve an inline link (isocpp#1933) Avoid ending the sentence with a dangling "see". * C 32 (#5) * Update CppCoreGuidelines.md * Update CppCoreGuidelines.md * Update isocpp.dic * use snake casing * sake case naming * C 32 comments (#3) * F.16 ("in" parameters): Move Matrix example to F.20 (return values) (isocpp#1922) The `Matrix` example and the notes about assignment appear off-topic in rule F.16, as F.16 is specifically about "in" parameters. With help from Sergey Zubkov. * SL.io.50 (Avoid `endl`): Mention string streams (isocpp#1920) Explicitly mentioned string streams as `endl` insertions into string streams do actually occur in the wild. With help from Sergey Zubkov. * Extended E.16 to include copy ctor for exception type, closes isocpp#1921 * Fix GitHub Actions build warnings, Marker style should be `*` (isocpp#1925) * restored reference * Added references to note Co-authored-by: Niels Dekker <[email protected]> Co-authored-by: Herb Sutter <[email protected]> Co-authored-by: Niels Dekker <[email protected]> Co-authored-by: Herb Sutter <[email protected]> Co-authored-by: Niels Dekker <[email protected]> Co-authored-by: Herb Sutter <[email protected]> Co-authored-by: Francisco Moretti <[email protected]> Co-authored-by: Sven van Haastregt <[email protected]>

* Update CppCoreGuidelines.md * Update CppCoreGuidelines.md * Update isocpp.dic * use snake casing * sake case naming * C 32 comments (#3) * F.16 ("in" parameters): Move Matrix example to F.20 (return values) (#1922) The `Matrix` example and the notes about assignment appear off-topic in rule F.16, as F.16 is specifically about "in" parameters. With help from Sergey Zubkov. * SL.io.50 (Avoid `endl`): Mention string streams (#1920) Explicitly mentioned string streams as `endl` insertions into string streams do actually occur in the wild. With help from Sergey Zubkov. * Extended E.16 to include copy ctor for exception type, closes #1921 * Fix GitHub Actions build warnings, Marker style should be `*` (#1925) * restored reference * Added references to note Co-authored-by: Niels Dekker <[email protected]> Co-authored-by: Herb Sutter <[email protected]> Co-authored-by: Niels Dekker <[email protected]> Co-authored-by: Herb Sutter <[email protected]>

N-Dekker force-pushed the SL.io.50-Mention-string-streams branch from bbdf585 to 8b750f4 Compare June 6, 2022 09:49

SL.io.50 (Avoid endl): Mention string streams

3503b5a

Explicitly mentioned string streams as `endl` insertions into string streams do actually occur in the wild. With help from Sergey Zubkov.

N-Dekker force-pushed the SL.io.50-Mention-string-streams branch from 8b750f4 to 3503b5a Compare June 6, 2022 09:54

BenjamenMeyer reviewed Jun 6, 2022

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jwakely approved these changes Jun 6, 2022

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hsutter merged commit 9ead2c4 into isocpp:master Jun 13, 2022

hsutter assigned jwakely and cubbimew Jun 13, 2022

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SL.io.50 (Avoid `endl`): Mention string streams #1920

SL.io.50 (Avoid `endl`): Mention string streams #1920

N-Dekker commented Jun 2, 2022 •

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cubbimew commented Jun 6, 2022

N-Dekker commented Jun 6, 2022 •

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BenjamenMeyer Jun 6, 2022

N-Dekker Jun 7, 2022

BenjamenMeyer Jun 7, 2022

jwakely Jun 7, 2022

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N-Dekker Jun 7, 2022

BenjamenMeyer commented Jun 6, 2022

jleffler commented Jun 7, 2022 via email

hsutter commented Jun 13, 2022

SL.io.50 (Avoid endl): Mention string streams #1920

SL.io.50 (Avoid endl): Mention string streams #1920

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hsutter commented Jun 13, 2022

SL.io.50 (Avoid `endl`): Mention string streams #1920

SL.io.50 (Avoid `endl`): Mention string streams #1920

N-Dekker commented Jun 2, 2022 •

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