IFS open() and existing files not truncating

["Robin Coles" <robin@xxxxxxxxxxxx>]

While the IFS code is under discussion, I'm writing a program to create
a file on the IFS for emailing, and have shamelessly plagiarised Scott's
code, which works fine, but....

If I open the file as:
     c                   eval      oflag = O_CREAT+O_WRONLY + O_CODEPAGE

     ** set mode to All

     c                   eval      omode = S_IRWXU + S_IRWXG + S_IRWXO

     c                   eval      fd = open(p_filename: oflag: omode:
     c                                      CP_ASCII)

I was expecting the file to be created if it didn't exist, and
completely overwritten if it did.

I ran it once and the file was created OK.  I inserted 2 extra lines
using EDTF and ran it again, and it's effectively updated the existing
lines (it writes a timestamp so I know I'm not going completely mad) and
left the manually inserted lines there.

Is this correct?  If so, I'll add an unlink() but I didn't think that
would be needed.

Cheers
Rob