Convert function to read from string instead of file in C

Posted by Dusty on Stack Overflow See other posts from Stack Overflow or by Dusty
Published on 2010-03-15T21:43:43Z Indexed on 2010/03/15 21:59 UTC
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I've been tasked with updating a function which currently reads in a configuration file from disk and populates a structure:

static int LoadFromFile(FILE *Stream, ConfigStructure *cs)
{
  int tempInt;

   ...

  if ( fscanf( Stream, "Version: %d\n",&tempInt) != 1 )
  {
    printf("Unable to read version number\n");
    return 0;
  }
  cs->Version = tempInt;
   ...

}

to one which allows us to bypass writing the configuration to disk and instead pass it directly in memory, roughly equivalent to this:

static int LoadFromString(char *Stream, ConfigStructure *cs)

A few things to note:

  • The current LoadFromFile function is incredibly dense and complex, reading dozens of versions of the config file in a backward compatible manner, which makes duplication of the overall logic quite a pain.
  • The functions that generate the config file and those that read it originate in totally different parts of the old system and therefore don't share any data structures so I can't pass those directly. I could potentially write a wrapper, but again, it would need to handle any structure passed in in a backwards compatible manner.
  • I'm tempted to just pass the file as is in as a string (as in the prototype above) and convert all the fscanf's to sscanf's but then I have to handle incrementing the pointer along (and potentially dealing with buffer overrun errors) manually.
  • This has to remain in C, so no C++ functionality like streams can help here

Am I missing a better option? Is there some way to create a FILE * that actually just points to a location in memory instead of on disk? Any pointers, suggestions or other help is greatly appreciated.

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