[boost] RE: IO Formatters and lexical_cast

From: Reece Dunn (msclrhd_at_[hidden])
Date: 2004-03-12 07:42:00

Roland Richter wrote:

>Reece,

>  I just checked out outfmt from the sandbox CVS and did some
>  tests to see whether it works together with lexical_cast.
>  The general idea is this:

>  Since lexical_cast internally uses a stringstream and its
>  associated operators>> and <<, it should be possible to
>  cast each type for which these operators are defined;
>  and since outfmt defines <</>> for STL container types,
>  I tried to combine them in order to convert between strings
>  and STL containers.

>  After some hassle, it works (under MS VC++ 7.0); see the
>  attachment. Issues:

>  1) For reasons I don't completely understand, the compiler
>     could not find operator<< from stl_io_basic.hpp when
>     compiling lexical_cast.hpp. I had to hack detail/stl_io_basic.hpp
>     and put everything in namespace boost::detail (where
>     lexical_stream lives).

>     BTW, I'm not happy that stl_io.hpp includes everything from
>     vector to slist, and that so much code is put into the global
>     namespace.

I am aware of this and am working on splitting the code into files like 
<boost/outfmt/stl/vector.hpp>, etc. There are three main areas that need to 
be split:

[1] The STL I/O code
[2] The type identification code
[3] The get/put helpers for pair-like objects

I have got a version of this to work with MS VC 7.x, but I have a 
compilation problem on borland and GCC 2.95.3-5 is generating a "signal 13" 
message on the regression tests (I think this is my cygwin setup, but 
haven't verified this). I have since been busy and haven't had a chance to 
look into these.

I shall move the inserters and extractors to the boost::detail namespace and 
will look into the lexical_cast problem.

>  2) The output operator puts spaces after '[', before ']',
>     and after each ','; whereas the input operator expects
>     no spaces at all; if spaces were present, a bad_lexical_cast
>     exception was thrown. I think it is really important that
>     operator>> can deal with an output which was generated by <<;
>     stated in terms of lexical_cast,
>
>        lexical_cast<T>( lexical_cast<string>( t ) ) == t
>
>     should hold for any T t.

I stripped and skipped the spaces during the read operation to allow for the 
read operation to accommodate input variations, e.g. [ a, b ]; [a, b] and [ 
a,b ] would be read by the same formatter, making it easier to interoperate 
with data generated from other sources. I could make this a configurable 
option that does not strip the spaces by default.

This should work. If you have examples where it doesn't, please let me know 
and I can add it into the regression tests.

NOTE: There is a known defect when handling string data. This may be 
generating the problem you are encountering. If you run my regression tests 
(libs/outfmt/test/generate.sh) you should see it as a fail. I am aware of 
the problem and am looking into it. (This is made more difficult because the 
solution I implemented doesn't work with Borland :()

>  I intend to do some further tests, and to give more feedback during
>  the IO Formatters formal review (no date is fixed yet, or is it?)

Thanks. I appreciate the feedback. I would like to get the string

>// Copyright Roland Richter 2004.
>// Distributed under the Boost Software License, Version 1.0.
>// (See accompanying file LICENSE_1_0.txt
>//  or copy at http://www.boost.org/LICENSE_1_0.txt)
>
>#include <boost/test/minimal.hpp>
>
>#include <vector>
>#include <string>
>
>#include <iostream>
>
>#include <boost/lexical_cast.hpp>
>#include <boost/outfmt/stl_io.hpp>
>
>// 1) Namespace problem:
>// e:\lib\boost_1_31_0\boost\lexical_cast.hpp(144): error C2679: binary 
>'<<' :
>//   no operator found which takes a right-hand operand of type 'const 
>_STL::vector<_Tp,_Alloc>' (or there is no acceptable conversion)
>//        with
>//        [
>//            _Tp=double,
>//            _Alloc=_STL::allocator<double>
>//        ]
>//
>// => move everything in boost/outfmt/detail/stl_io_basic.hpp into 
>namespace boost::detail
>
>// 2) operator<< puts spaces after '[' and ',', whereas operator>> expects
>//    no spaces at all (otherwise, bad_lexical_cast is thrown).
>
>
>void lexical_cast_and_outfmt_test()
>{
>   double foos[] = {0.7016, 0.9943, 1.3441, 1.1637, 0.5994, 0.0000, 
>0.0000};
>   std::vector<double> fooVec( foos, foos + 7 );
>
>   std::string fooStr( "[ 0.7016, 0.9943, 1.3441, 1.1637, 0.5994, 0, 0 ]" 
>);
>
>   // Output
>   std::string castedStr = boost::lexical_cast<std::string>( fooVec );
>   BOOST_CHECK( castedStr == fooStr );
>
>   std::string fooStr_WithoutSpaces( 
>"[0.7016,0.9943,1.3441,1.1637,0.5994,0,0]" );
>
>   // Input
>   std::vector<double> castedVec
>     = boost::lexical_cast< std::vector<double> >( fooStr_WithoutSpaces );
>   BOOST_CHECK( castedVec == fooVec );
>}
>
>
>int test_main( int, char *[] )
>{
>   lexical_cast_and_outfmt_test();
>
>   return 0;
>}

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