Re: [boost] Interest in simple unformatted binary stream I/O?

Subject: Re: [boost] Interest in simple unformatted binary stream I/O?
From: Max Sobolev (macsmr_at_[hidden])
Date: 2011-04-27 07:28:42

On 24.04.2011 16:12, Beman Dawes wrote:
> There have been many requests on Boost and various C++ newsgroups for
> unformatted binary I/O. For example, in 2003 Neal Becker wrote:
>
>       I wonder if anyone has code for implementing unformatted I/O?
> What I have in mind is
>       for the simple case where the application that reads data knows
> the data types, so
>       this is not as complicated as the general marshalling situation.
>
> This proposal provides a very simple solution that works with standard
> library input and output streams. The one caveat is that the stream
> must be opened with filemode std::ios_base::binary to avoid certain
> data values being treated as line endings.
>
> int main()
> {
>    fstream f("binary_stream_example.dat",
>      std::ios_base::trunc | std::ios_base::in | std::ios_base::out |
> std::ios_base::binary);
>
>    int32_t x = 0x01020304;
>    int32_t y = 0;
>
>    f<<  bin(x);  // write 4 bytes
>    f.seekg(0);
>    f>>  bin(y);   // read 4 bytes
>
>    BOOST_ASSERT(x == y);
>
>    return 0;
> }
>
> For docs, header, and example code, see
> http://mysite.verizon.net/beman/binary_stream/binary_stream.html
> http://mysite.verizon.net/beman/binary_stream/binary_stream.hpp
> http://mysite.verizon.net/beman/binary_stream/binary_stream_example.cpp
>
> Is there interest in this for Boost?
>
> It seems way too small and simple to be a whole library itself. Are
> there any ideas where it should live and what namespace it should be
> in?
>
> --Beman

For such tasks i use very basic tool in the form of 2 overloaded 
function templates named raw_cast<>() that converts from native 
representation of a fundamental type (except void) to its raw-byte 
representation, and vice versa.

raw_cast<>() implementation (raw_cast.hpp): http://codepad.org/x47pQiNA

code example: http://codepad.org/5y3RPj9r

[output (on a little-endian machine):
67305985 (raw: 1 2 3 4 [little endian]; 4 3 2 1 [big endian])

raw: 0 0 0 0 0 0 f0 3f 7f 0 0 0 58 ff ff ff ff 71 5 0
native: {1 : 127 : X : 0xffffffff : q : 5}
--end]

(Code works as is on linux. On other platforms there should be defined 
BYTE_ORDER macro that equals to BIG_ENDIAN or something else; otherwise 
machine's byte ordering will be interpreted as little endian.)

___________________
I think the following code (used in raw_cast<>() implementation) isn't 
correct:

char const* const begin = reinterpret_cast<char const* const>(&value);
char const* const end   = reinterpret_cast<char const* const>(&value) + 
sizeof(T);

(Byte representation of any trivial copyable type isn't array actually.)

if so, boost::reverse_iterator<> should be replaced below (in code) to 
an iterator without 'past-the-end' semantics

-- 
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