Fix #14743 (New check: ftell() result is unspecified when file is opened in mode "t") by damorinCan · Pull Request #8360 · cppcheck-opensource/cppcheck

damorinCan · 2026-03-21T16:45:33Z

Some legacy tools stopped suddenly working after 20+ years.

https://stackoverflow.com/questions/79762122/ftell-no-more-returning-the-correct-offset-on-a-text-file-with-windows-11-ente

Trac ticket: https://trac.cppcheck.net/ticket/14743#ticket

chrchr-github · 2026-03-21T18:29:28Z

Thanks for your contribution.
As far as I can tell, this has nothing to do with Windows 11, but rather the C11 spec of ftell(), right? So the title of the PR should be adjusted.
Please add a test.

damorinCan · 2026-03-21T21:42:01Z

So the title of the PR should be adjusted.

Title now including reference to C11 and removed reference to Windows 11.

Please add a test.

I added a test in test/testio.cpp. Anything missing in it ?

chrchr-github · 2026-03-21T21:48:12Z

Please add a test.

I added a test in test/testio.cpp. Anything missing in it ?

Thanks, I must have missed that.

chrchr-github · 2026-03-24T08:08:23Z

Ping @danmar

danmar

I feel we need to have a ticket for this in trac

it feels like it should be added to the release notes as a "new check" ?

danmar · 2026-04-13T10:56:59Z

I have tried to add some descriptions about some of our checkers here:
https://github.com/danmar/cppcheck/tree/main/man/checkers

Ideally that would contain descriptions for all our checkers but due to lack-of-resources it does not.

If you can add a corresponding file for this checking that would be great.

sonarqubecloud · 2026-04-18T16:33:26Z

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

danmar · 2026-04-24T20:15:31Z

We need a ticket in trac for this.

Can you please tell me what you think the summary and description should be and we can create it..

damorinCan · 2026-05-02T17:38:04Z

We need a ticket in trac for this.

Can you please tell me what you think the summary and description should be and we can create it..

Thanks, I lost my login/password (last time was years ago). What about this:

[ftell() is no more returning the correct offset on a text file with Windows 11 compared to Linux.

danmar · 2026-05-02T20:14:01Z

Thanks, I lost my login/password (last time was years ago). What about this:

do you remember your username? If you send me a new htpasswd hash via email I can update..

danmar · 2026-05-11T09:33:26Z

The PR title should be something like:

Fix #14743 (ftell() not consistent in C11)

I would like that the PR title and ticket title are consistent. and well imho the fundamental issue is not that linux/windows does not have the same behavior. the fundamental issue is that the behavior is implementation defined. it's possible you can have different behavior when using the same compiler but different volume type, compiler flags, etc..

damorinCan · 2026-05-11T22:16:00Z

Hi, I tried to edit the ticket title but it's not possible so I made the PR title the same as the ticket. Robert Le lun. 11 mai 2026 à 05:33, Daniel Marjamäki ***@***.***> a écrit :

…

*danmar* left a comment (cppcheck-opensource/cppcheck#8360) <#8360 (comment)> The PR title should be something like: Fix #14743 (ftell() not consistent in C11) I would like that the PR title and ticket title are consistent. — Reply to this email directly, view it on GitHub <#8360 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AB2AXDMB3H3KXMOCKNN3DTD42GM7ZAVCNFSM6AAAAACW2EKWFWVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHM2DIMJZGMYDOMRVHE> . Triage notifications on the go with GitHub Mobile for iOS <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android <https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub>. You are receiving this because you authored the thread.Message ID: ***@***.***>

danmar · 2026-05-12T19:39:11Z

+void CheckIO::ftellFileError(const Token *tok)
+{
+    reportError(tok, Severity::portability,
+                "ftellTextModeFile", "The ftell function obtains the current value of the file position indicator"


sorry but I want to change...

This is not a good warning message. How about:

ftell() result is unspecified when file is opened in mode "t"

I want that the standard text is quoted in the ftellTextModeFile.md file.

danmar · 2026-05-13T07:07:02Z

Could you add a note about this in the releasenotes? In my opinion we can say it's a new check. Technically it's not but it's a completely new type of warning.

…"t". New changes: - Added missing string related to new check - Added checker description for ftellTextModeFile - Updated releasenotes.txt with new check

danmar · 2026-05-27T11:10:39Z

+     FILE *f = fopen("Example.txt", "rt");
+     if (f)
+     {
+        int position;


these variables position and st are not needed

danmar · 2026-05-27T11:12:34Z

+     if (f)
+     {
+        fseek(f, 0, SEEK_END);
+        printf( "Offset %d\n", ftell(f);


I suggest that the "After" example matches the "Good" example except the file mode.

danmar · 2026-05-27T11:15:08Z

+
+## Description
+
+This checker detects the use of ftell() on a file open in text (or translate) mode. The text mode is not consistent


I would like that we provide the text from the standard . You only reference the windows documentation, that is not as strong and important as the standard. and also I feel it's misleading to point at windows this is an issue you should be aware of no matter what platform you compile on.

damorinCan changed the title ~~ftell() have a different behavior in Windows 11 than before.~~ ftell() not consistent in C11 Mar 21, 2026

danmar reviewed Apr 9, 2026

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Comment thread lib/checkio.cpp Outdated

Comment thread test/testio.cpp Outdated

danmar reviewed Apr 24, 2026

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Comment thread man/checkers/ftellTextModeFile.md Outdated

Comment thread lib/checkio.h Outdated

danmar reviewed Apr 24, 2026

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Comment thread test/testio.cpp Outdated

Comment thread man/checkers/ftellTextModeFile.md Outdated

damorinCan changed the title ~~ftell() not consistent in C11~~ ftell() not consistent in between Linux/Unix and Windows when file is opened in mode "t" May 11, 2026

danmar changed the title ~~ftell() not consistent in between Linux/Unix and Windows when file is opened in mode "t"~~ Fix #14743 (ftell() not consistent when file is opened in mode "t") May 12, 2026

danmar reviewed May 12, 2026

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danmar changed the title ~~Fix #14743 (ftell() not consistent when file is opened in mode "t")~~ Fix #14743 (New check: ftell() result is unspecified when file is opened in mode "t") May 13, 2026

danmar reviewed May 13, 2026

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Comment thread man/checkers/ftellTextModeFile.md Outdated

danmar reviewed May 13, 2026

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Comment thread man/checkers/ftellTextModeFile.md

damorinCan force-pushed the CWE474_ftell branch from c103823 to bd6a132 Compare May 18, 2026 15:38

New check: ftell() result is unspecified when file is opened in mode …

d3f0a5a

…"t". New changes: - Added missing string related to new check - Added checker description for ftellTextModeFile - Updated releasenotes.txt with new check

damorinCan force-pushed the CWE474_ftell branch from bd6a132 to d3f0a5a Compare May 23, 2026 14:05

danmar reviewed May 27, 2026

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		## Description

		This checker detects the use of ftell() on a file open in text (or translate) mode. The text mode is not consistent

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damorinCan commented Mar 21, 2026 •

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