Re: runtime type issues (or, reading complicated logfiles)

From: (Carl Barron)
Mon, 29 Oct 2007 02:52:50 CST
Benjamin Collins <> wrote:

  /* ... */
  std::ifstream ifs("filename");
  common_header info;
      ifs >> info;
      void *header = read_header(ifs, info); /* allocate header
here, and read log using ifs */

      /* do stuff with 'info' and 'header' */

What has me thinking is how to handle allocation of the format
header. Right now, I'm contemplating having read_header allocate the
header and return it as a void*, but I'd rather be able to use
std::auto_ptr or

the common heaser determins what to read and which function to use, so
a table of boost or tr1 function allows a table of functors of the
same signature to be stored in an array or map , or tr1::usnsorted_map
to be used for lookup

   read the common header
   lookup proper function and call it

class log_reader
    typdef std::tr1::function<void(std::istream &,const common_header
&)> function_type;
    typedef std::vector<function_type> table_type;
    table_type perform;
     log_reader() {/* build table */}
     void operator () (std::istream &in)
        common_header info;
        while(in >> info)

// ...

   log_reader reader;
 should work with table_type
std::vector<function_type>,std::map<int,function_type>, or

the functions read the sub header and perform according to subsection's

  probably easier to maintain than a cascade of if's.

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