[boost] [iostreams] basic_buffer int usage

Subject: [boost] [iostreams] basic_buffer int usage
From: Judson Weissert (judson_at_[hidden])
Date: 2011-08-12 09:32:38

Hello,

I was working with some boost::iostreams code for compressing and uncompressing streams of data when I encountered an interesting type conversion warning.

Within buffer.hpp in the iostreams library (boost/iostreams/detail folder), the constructors accept an int buffer_size and assign it to std::streamsize size_. Upon further investigation, I learned that this was intentional as of r27330 (Log msg: "made all buffer size params ints so that int literals can be used without interfering with overload resolution").

Here is some example code that triggers the same warnings I was receiving:

// Tested with boost 1.46.1
// Compiler Microsoft VC2010 SP1.
// Compiled with cl /EHsc /W3 repro.cpp

#include <boost/iostreams/copy.hpp>
#include <boost/iostreams/device/array.hpp>
#include <boost/iostreams/filtering_streambuf.hpp>

int
main (int, char *[])
{
  static const char b[] = { 'A', 'B', 'C' };
  boost::iostreams::array_source as (b, 3);
  boost::iostreams::filtering_streambuf <boost::iostreams::input> in;
  in.push (as);

  // This line generates a 'std::streamsize' to 'int' warning.
  // See also boost/iostreams/detail/buffer.hpp
  boost::iostreams::copy (in, std::cout);

  return 0;
}

I am not completely sure what overload resolution is taking place, I only see a default constructor and a constructor that takes a buffer size. What am I missing?

I posted approximately a week ago on this topic, but I don't think it made it to the list. Forgive me if this is a repost, I modified the content of the message since I learned more about the subject in the meantime.

Thanks,

Judson Weissert