gistfile1.txt

json::value
parse_file( char const* filename )
{
    json::error_code ec;
    auto f = std::fopen( filename, "r" );
    if( ! f )
    {
        ec.assign( errno, json::generic_category() );
        throw json::system_error(ec);
    }
    json::parser p;
    p.start();
    do
    {
        char buf[4096];

        // Read from the file into our buffer.
        auto const nread = fread( buf, 1, sizeof(buf), f );
        if( std::ferror(f) )
        {
            ec.assign( errno, json::generic_category() );
            throw json::system_error(ec);
        }

        auto nparsed = p.write_some( buf, nread, ec);

        // Make sure we use all the characters in the file.
        if( ! ec && nparsed < nread )
            nparsed = p.write_some( buf + nparsed, sizeof(buf) - nparsed, ec );

        if( ec )
            throw json::system_error(ec);
    }
    while( ! std::feof(f) );

    // Tell the parser there is no more serialized JSON.
    p.write_eof(ec);
    if( ec )
        throw json::system_error(ec);

    return p.release();
}