New: difftime(3) may suggest that time_t can be a non-arithmetic type
https://bugzilla.kernel.org/show_bug.cgi?id=46731
Summary: difftime(3) may suggest that time_t can be a
non-arithmetic type
Product: Documentation
Version: unspecified
Platform: All
OS/Version: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: man-pages
AssignedTo: documentation_man-pages-ztI5WcYan/[email protected]
ReportedBy: [email protected]
Regression: No
Created an attachment (id=78851)
--> (https://bugzilla.kernel.org/attachment.cgi?id=78851)
Patch changing the wording to the more exact problem
The difftime(3) manpage[1] states:
NOTES
On a POSIX system, time_t is an arithmetic type, and one could just
define
#define difftime(t1,t0) (double)(t1 - t0)
when the possible overflow in the subtraction is not a concern. On
other
systems, the data type time_t might use some other encoding where subtraction doesn't work directly.
---
When I first read this, I got confused that time_t may actually be a non-arithmetic type. But the C99 standard explicitly lists (in 7.23.1):
3 The types declared are size_t (described in 7.17); clock_t and time_t which
are arithmetic types capable of representing times
---
I think that particular paragraphs should be re-worked to explicitly state what differences can arise in time_t implementations and what is the reason that they can't be used to compute time differences. As far as I understand, the only issue is that time_t can express time in units other than seconds.
I'm attaching a patch with my wording for that.
[1]:http://man7.org/linux/man-pages/man3/difftime.3.html
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[Bug 46731] difftime(3) may suggest that time_t can be a non-arithmetic type
In reply to a message not in the archivehttps://bugzilla.kernel.org/show_bug.cgi?id=46731
Michael Kerrisk <[email protected]> changed:
What |Removed |Added
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