How do I specify a path with libcurl for file uploads/downloads? or What's the correct way to specify

Ah, the classic libcurl specify path confusion. Here’s the deal:

- `CURLOPT_READDATA`/`CURLOPT_WRITEDATA` expect a FILE* handle, not a path string.
- You *must* open the file in the correct mode (`"rb"` for read, `"wb"` for write).
- Path separators? libcurl is cool with `/` everywhere, even Windows. But if you’re constructing paths, use `\\` on Windows for consistency.

Example snippet:
```c
FILE *dl = fopen("output.txt", "wb");
curl_easy_setopt(curl, CURLOPT_WRITEDATA, dl);
```
Don’t forget error checking!