Re: [boost] Serializer and when to stop

From: Victor A. Wagner Jr. (vawjr_at_[hidden])
Date: 2004-06-07 09:00:52

your input loop has a problem!!
you test for eof() then attempt a read and do NOT test the results of the read!
two fixes given below

At Saturday 2004-06-05 18:30, you wrote:
>I'm using boost::serializer between two programs: the first creates the 
>data then serializes it, the second loads that data in and analyzes it.
>
>When I had just 420 data samples it all worked fine: I create a 
>vector<Sample> in memory, serialized it and loaded it in the other side. 
>When I moved to 7000 data samples the first program, the creator, sucked 
>all the memory from the machine and then some.
>
>So I moved to serializing each data sample as it was created. To read it 
>back in I changed my code from this:
>
>std::ifstream input_file(fname,std::ios::binary);
>boost::archive::binary_iarchive archive(input_file);
>std::vector<Sample> samples;
>archive>>samples;
>input_file.close();
>
>
>Into this:
>
>std::ifstream input_file(fname,std::ios::binary);
>boost::archive::binary_iarchive archive(input_file);
>
>std::vector<Sample> samples;
>samples.reserve(8000);
>
>while(!input_file.eof()){
>         Sample s;
>         archive>>s;

replace the above line with:
         if(archive>>s)

>         samples.push_back(s);
>         }

or rewrite the loop:

Sample s;
while(archive >> s) samples.push_back(s);

if it's important that s be destructed at loop end, simply enclose the 
above two lines in { }

>input_file.close();
>
>
>But every time it fails with an assert [1]. This seems to be when it has 
>reached end of file. I cannot know in advance how many data samples I'll 
>write to disk, so it seems I have three options:
>   A: Make a special "zero" version of Sample to mark end of file
>   B: At end of program 1 write the number of samples to a special file, 
> and read that in before starting the above loop, so I know when to stop.
>   C: Alter the serializer class to throw exception instead of an assert; 
> I can then catch it and carry on.
>
>
>What is the best way? Is adding a terminator byte to boost::serializer an 
>option (i.e. so I don't have to make a terminator version of each data 
>structure I want to serialize).
>
>Incidentally my above loop does a copy of each sample as it adds it to the 
>vector. Is the above code going to be common enough to make it worth 
>including into boost::serializer as a helper function, which could then be 
>optimized with in-place construction or something clever like that? (And 
>then it could handle the termination handling itself as well.)
>
>Darren
>
>
>
>
>[1]:
>/usr/local/src/boost_1_31_0/boost/archive/basic_binary_iprimitive.hpp:119: 
>void boost::archive::basic_binary_iprimitive<Archive, 
>IStream>::load_binary(void*, unsigned int) [with Archive = 
>boost::archive::binary_iarchive, IStream = std::basic_istream<char, 
>std::char_traits<char> >]: Assertion `count == 
>static_cast<size_t>(is.gcount())' failed.
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Victor A. Wagner Jr.      http://rudbek.com
The five most dangerous words in the English language:
               "There oughta be a law"