On 4/13/20 11:53 AM, Freddie Akeroyd - UKRI STFC via Core-talk wrote:
> Hi Michael,
>
> I ran your code through the visual studio pre-processor to see what it generated and it was:
>
> do{ if((logerr).test(::pvxs::Level::Info)) ::pvxs::detail:: _log_printf(unsigned(::pvxs::Level::Info), "%s " "Enter loop worker for %p\n", base.get(), "" ); }while(0);
>
> So the "" argument is being moved to the end. I removed the string concatenation and the problem was still there. I moved the "" argument to before the FMT i.e.
>
> _log_printf(unsigned(LVL), "", "%s " FMT, __VA_ARGS__)
>
> And then it seemed to pre-process correctly, so I think you may have discovered an interesting "feature" of the pre-processor
Wow, I would never have guessed this...
Thank you Freddie!
> Regards,
>
> Freddie
>
> -----Original Message-----
> From: Core-talk <core-talk-bounces at aps.anl.gov> On Behalf Of Michael Davidsaver via Core-talk
> Sent: 13 April 2020 08:29
> To: EPICS core-talk <core-talk at aps.anl.gov>
> Subject: MSVC printf/vararg weirdness
>
> All,
>
> I've run up against a strange behavior with MSVC. I've reduced the problem somewhat, but which I'm not sure how to proceed. This might have something to do with the MSVC pre-processor, implicit concatenation of string constants, or maybe vararg functions.
>
> It has to do with how I'm trying to do logging. At core I have a function:
>
>> void _log_printf(unsigned lvl, const char* fmt, ...);
>
> which internally calls errlogVprintf()
>
> I'm calling it through two levels of macro. eg.
>
>> #define log_info_printf(LOGGER, ...) log_printf(LOGGER,
>> ::pvxs::Level::Info, __VA_ARGS__)
>
>> #define log_printf(LOGGER, LVL, FMT, ...) do{ \
>> if((LOGGER).test(LVL)) \
>> ::pvxs::detail:: _log_printf(unsigned(LVL), "%s " FMT, "",
>> __VA_ARGS__); \
>> }while(0)
>
> called like:
>
>> log_info_printf(logerr, "Enter loop worker for %p\n", base.get());
>
> The reason for the second level of macro is that I'd like to prefix each log line with some extra information, including a timestamp, in a way which can't be split.
> (as could happen if I called errlogPrintf() twice)
>
> The above is already a reduced case. The empty string constant "" after FMT will be replaced with a char* returned by a function (a thread local buffer). However, I can't get that far.
>
> The above, with the empty string constant, is somehow corrupting output and crashing.
> eg.
>
>> `b"l Enter loop worker for 00007FFA6C34DCC0 `b"l Enter loop worker
>> for 00007FFA6C34DCC0
>
> If I change the log_printf macro as follows, then everything is fine (sans timestamp).
>
>> #define log_printf(LOGGER, LVL, FMT, ...) do{ \
>> if((LOGGER).test(LVL)) \
>> ::pvxs::detail:: _log_printf(unsigned(LVL), FMT, __VA_ARGS__);
>> \
>> }while(0)
>
> Does anyone have an idea of what is going on here?
>
> I don't think I'm depending on any GCC-isms here. (eg. __VA_ARGS__ always has at least one argument) And '"%s " FMT' should be taking advantage of automatic concatenation of string constants.
>
> I'm seeing this on appveyor with the MSVC 2019, 2017, and 2015.
> mingw builds work fine.
>
> https://ci.appveyor.com/project/mdavidsaver/pvxs
>
> the full version I'm starting from (and would like to end with).
>
> https://github.com/mdavidsaver/pvxs/blob/e2a7e5e451a06e3865b8684e747dfaa6026a6e15/src/pvxs/log.h#L77-L80
>
- References:
- MSVC printf/vararg weirdness Michael Davidsaver via Core-talk
- RE: MSVC printf/vararg weirdness Freddie Akeroyd - UKRI STFC via Core-talk
- Navigate by Date:
- Prev:
RE: AppVeyor issue Freddie Akeroyd - UKRI STFC via Core-talk
- Next:
[Merge] ~info-martin-konrad/epics-base:explicitly-specify-appveyor-worker-image into epics-base:3.15 Martin Konrad via Core-talk
- Index:
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
<2020>
2021
2022
2023
2024
- Navigate by Thread:
- Prev:
RE: MSVC printf/vararg weirdness Freddie Akeroyd - UKRI STFC via Core-talk
- Next:
Re: MSVC printf/vararg weirdness Michael Davidsaver via Core-talk
- Index:
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
<2020>
2021
2022
2023
2024
|