Re: sizeof with g++ > 5.2

[Michael Davidsaver via Core-talk <core-talk at aps.anl.gov>]

> mPollQueue(1, sizeof(acquisition_t))

https://github.com/search?q=org%3AareaDetector+mPollQueue&type=Code

So you're asking about byte-wise copying a std::string into
an epicsMessageQueue?

This is, and has always been, a really bad idea.  It isn't safe to
mix C and C++ like this.  You'll need to use something other than
epicsMessageQueue, or replace use of std::string with a plain char[].

I generally use a combination of std::deque, an epicsEvent, and an epicsMutex
to keep it all reentrant.


On 3/4/20 10:22 AM, Gofron, Kazimierz via Core-talk wrote:
> Hi,
> 
> Since base is written in C, and many drivers are written in C++, we are seeing some issues for string, as discussed below.
> 
> https://epics.anl.gov/tech-talk/2020/msg00515.php
> 
>  
> 
> The g++ on Debian9 uses newer compiler than g++ > 5.2, and reports sizeof(string) up to 15.
> 
> http://www.cplusplus.com/forum/beginner/173925/
> 
> sizeof(std::string), in-object space for small string storage:
> ```
> GNU libstdc++ (conforming implementation, GCC 5.2 or later): *32, 15*
> LLVM libc++: *24, 22*
> Microsoft msc++ 19.00 (VS 2015): *28, 15*
> 
> *```*
> 
>  
> 
> Is there a replacement / better way to use sizeof?
> 
> mPollQueue(1, sizeof(acquisition_t))
> 
>  
> 
> Kazimierz Gofron
> 
> NSLS-II Controls Group
> 
> Brookhaven National Laboratory
> 
> (p) +1 (631) 344 5283
> 
> (f) +1 (631) 344 8085
> 
> (e) kgofron at bnl.gov <mailto:kgofron at bnl.gov>
> 
> (w) www.bnl.gov/nsls2 <http://www.bnl.gov/nsls2>
> 
>  
>