> For the complete documentation index, see [llms.txt](https://eric-lo.gitbook.io/lab9-filesystem/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://eric-lo.gitbook.io/lab9-filesystem/accessing-fat-using-c/finding-next-cluster.md).

# Finding Next Cluster

After reading the current cluster, how can we advance to the next cluster?

**Answer**: by checking the FAT table. With the current cluster number, we can get the next cluster in FAT, or a EOF.

How can we know the terminating condition? There are three conditions in total. If we encounter these during search, that means it reaches the end.

1. End of File

   **EOF**

   (0x0ffffff8)
2. Damaged (Bad Cluster Mark) (0x0ffffff7)
3. Unallocated (0x0)

```c
uint32_t next_cluster(FILE *fp, off_t fat_offset, uint32_t current_cluster) {
    uint32_t next_cluster_number = 0;
    fseek(fp, fat_offset + current_cluster * sizeof next_cluster_number,
          SEEK_SET);
    size_t ret = fread(&next_cluster_number, 1, sizeof next_cluster_number, fp);
    return next_cluster_number;
}
```