Why is the beginning of a C file stream called `SEEK_SET`?

Question

There are three origin constants you can use in functions like fseek to determine from where your offset is counted: SEEK_SET, SEEK_CUR, and SEEK_END. SEEK_CUR and SEEK_END seem self-explanatory to mean the current position and end of the file stream, but why is SEEK_SET used to mean the beginning? Why not something like SEEK_BEG?

Answer 1

Because you can add an offset. By using SEEK_SET, you can explicitly set an offset. (By adding it to the beginning)

From the manpage of fseek:

The new position, measured in bytes, is
obtained by adding offset bytes to the position specified by whence.
If whence is set to SEEK_SET, SEEK_CUR, or SEEK_END, the offset is
relative to the start of the file, the current position indicator, or
end-of-file, respectively.

From the manpage of lseek:

   SEEK_SET
          The file offset is set to offset bytes.

   SEEK_CUR
          The file offset is set to its current location plus offset
          bytes.

   SEEK_END
          The file offset is set to the size of the file plus offset
          bytes.