typedef struct Sprite {
     size_t offset;
     int size_x;
     int size_y;
     // etc
} Sprite;

std::list<Sprite *> LoadSprites(uint8_t *buf, size_t bufSize, char filenames[], int count)
{
      
     size_t currOffset = 0;
     size_t readed;
     int size_x;
     int size_y;
     std::list<Sprite *> sprites;
      
     for (int i = 0; i < count; i++) {
         FILE *sprite_file = fopen(filenames[i], "r");
         // for example - sprite is a file with sizes  
         // in first line and "raw rgb colors" at others
         if (fscanf(sprite_file, "%d %d\n", &size_x, &size_y) == 2 && size_x > 0 && size_y > 0) {
              
             if (currOffset + size_x * size_y >= bufSize) {
                 fprintf(stderr, "ERROR: Failed load sprites - not enough memory\n");
                 return sprites;
             }
              
             readed = 0;
             for (int j = 0; j < size_x * size_y; j++, currOffset++, readed++) {
                 int ch = fgetc(sprite_file);
                 if (ch != EOF)
                     buf[currOffset] = getchar();
                 else
                     break;
             }
              
             if (readed == size_x * size_y) {
                 Sprite *sprite = { currOffset, size_x, size_y };
                 sprites.push_back(sprite);
                 continue;
             }
             else {
                 currOffset -= readed;
             }
         }
         fprintf(stderr, "ERORR: Failed load sprite \"%s\"\n", filenames[i]);
     }
      
     return sprites;
}

struct NodesTable
{
        int nodesCount; // count of groups
        int *nodesSizes; // sizes of groups
        int tableSize; // size of this table
};

const int groupsCount = 3;
NodesTable nodesTable { groupsCount, new int[groupsCount], sizeof(int) * (groupsCount +  2) };

ifstream ifile("input");

// 1
ifile.seekg(nodesTable.tableSize, ios_base::beg);

// 2
ifile.seekg(nodesTable.tableSize + nodesTable.nodesSizes[0], ios_base::beg);
...