Re: [Boost-users] Accessing memory in shared segments

Subject: Re: [Boost-users] Accessing memory in shared segments
From: Andy Falanga (afalanga) (afalanga_at_[hidden])
Date: 2013-06-28 16:52:36

>From: Andy Falanga (afalanga) 
>Sent: Thursday, June 27, 2013 7:42 AM
>To: 'boost-users_at_[hidden]'
>Subject: Accessing memory in shared segments
>
>Hi,
>
>I have some code which shares data with shared memory.  To that end, I'm using >boost::interprocess:managed_shared_memory.  Without respect to scope and functions, what I have is >roughly:
>
>boost::interprocess::managed_shared_memory  sharedMem(boost::interprocess::create_only, 
> "SharedMemory", 4096);
>
>//later on
>u_int8_t* dataSegment = sharedMemory.construct<u_int8_t>("data")[5](0);
>char* string1 = sharedMemory.construct<char>("String 1")[50]('\0');
>// other stuff
>
>// placing stuff in the data segment
>for(int i(0); i < 5; i++) dataSegment[i] = anEarlierArray[i];
>
>
>// then, in other process read the data Segment
>char ary[5];
>for(int i(0); i< 5; i++) ary[i] = dataSegment.first[i];
>
>
>For whatever reason I couldn't simply access through dataSegment[n] notation.  The weirdest thing is, >the data is being read back to me in the reverse order that it should be.  For example, if 
>[0x2,0x4,0x7,0x1] is written I read it back as [0x1,0x7,0x4,x02] even though I'm writing and reading >in the same order.  Why is this?  What is it I'm missing about using shared memory?

Problem solved: it was between the keyboard and the chair.  Further debugging showed that the data wasn't being written in reverse (it made no sense that it would have been) but rather was a result of some HID libraries I'm using under the hood.

Posting this in case someone hits on this message while looking through the archives.

Andy