Question

I’m parsing some CSV data in C for the purposes of a Ruby extension. In order to pull out the data from each row I’m using sscanf as follows:

  char* line = RSTRING_PTR(arg);
  double price;
  double volume_remaining;
  unsigned int type_id, range, order_id, volume_entered, minimum_volume, duration, station_id, region_id, solar_system_id, jumps;
  char* issued;
  char* bid;
  printf("I got %s\n",line);
  int res = sscanf(line, "%lf,%lf,%u,%u,%u,%u,%u,%s,%s,%u,%u,%u,%u,%u", &price, &volume_remaining, &type_id, &range, &order_id, &volume_entered, &minimum_volume, bid, issued, &duration, &station_id, &region_id, &solar_system_id, &jumps);
  printf("I matched %d values\n", res);
  printf("I have price %f, vol_rem %f, type_id %d, range %d, order_id %d, vol_ent %d, min_vol %d, issued %s, bid %s, duration %d, station_id %d, region_id %d, solar_system_id %d, jumps %d, source %s \n",price, volume_remaining, type_id, range, order_id, volume_entered, minimum_volume, issued, bid, duration, station_id, region_id, solar_system_id, jumps, source); // and hash build follows below

Running it produces this:

I got 728499.93,437.0,2032,32767,1132932560,588,1,False,2009-05-24 19:52:08.000,90,60003760,10000002,30000142,0
I matched 7 values
I have price 728499.930000, vol_rem 437.000000, type_id 2032, range 32767, order_id 1132932560, vol_ent 588, min_vol 1, issued (null), bid (null), duration -1210229476, station_id 3001, region_id 3001, solar_system_id 1, jumps -1210299816

Note the null strings. Basically, it seems like sscanf is tripping on these for some reason. I can’t figure out why even having read the docs thoroughly. Any ideas?

Answer 1

Your character pointers are unitialized, and point to a random segment of memory. You must allocate a buffer for sscanf() to write to, and it must be big enough. (You’re lucky that didn’t segfault.) That second part is the hard part — scanf() might not be the right tool for the job here.