Boost C++ Libraries: Ticket #5139: Initial Stream Position in Boost.Interprocess.Vectorstream

anonymous — Sat, 29 Jan 2011 14:35:36 GMT

I think the problem is with boost::interprocess::basic_vectorstream::seekoff.

On line 284 of boost/interprocess/streams/vectorstream.hpp it reads:

Code highlighting:

    //Test for logic errors
    if(!in & !out)
       return pos_type(off_type(-1));
    else if((in && out) && (dir == std::ios_base::cur))
       return pos_type(off_type(-1));
    else if((in  && (!(m_mode & std::ios_base::in) || this->gptr() == 0)) ||
             (out && (!(m_mode & std::ios_base::out) || this->pptr() == 0)))
       return pos_type(off_type(-1));

This code doesn't account for the possibility that the internal vector is empty, and the user simply wants to get the current position (which should be 0.)

A possible fix would be:

Code highlighting:

//Test for logic errors
if (!in & !out)
   return pos_type(off_type(-1));
else if((in && out) && (dir == std::ios_base::cur))
   return pos_type(off_type(-1));
else if( (in && (!(m_mode & std::ios_base::in))) || (out && (!(m_mode & std::ios_base::out))))
   return pos_type(off_type(-1));
else if ((in && this->gptr() == 0) || (out && this->pptr() == 0))
   return off == 0 ? pos_type(off_type(0)) : pos_type(off_type(-1));

status changed; resolution set

Ion Gaztañaga — Fri, 01 Apr 2011 19:41:23 GMT

status new → closed
resolution → invalid

Sorry, but in MSVC7-1 it outputs -1,-1. I don't think there is any guarantee to return 0.

status, version changed; cc set; resolution deleted

superpacko@… — Mon, 20 Apr 2015 20:06:02 GMT

cc superpacko@… added
status closed → reopened
version Boost 1.45.0 → Boost 1.57.0
resolution invalid

This is happening in vs2013 as well if you dont provide a vector or you provide an empty one, tellp() returns -1. Is no good, it forces you to initialize with a vector with something inside, instead of just relying on that default position would be 0, since it is for both input and output and theres the possibility to write on it.

Ion Gaztañaga — Wed, 24 Jun 2015 14:05:02 GMT

The C++98 standard never guaranteed tellp() would return 0. It seems that after LWG Issue 453 returning zero is the agreed behaviour:

http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#453

Several compilers and implementation seems to have fixed this so it seems logical to port it to Interprocess streams.

status changed; resolution set

Ion Gaztañaga — Wed, 24 Jun 2015 14:22:31 GMT

status reopened → closed
resolution → fixed

Fixed in:

[develop e352a84] Fixed Trac #5139 ("Initial Stream Position in Boost.Interprocess.Vectorstream")

https://github.com/boostorg/interprocess/commit/e352a84dd2d31fcad14f721c8359d25a5f9dc9fc