Question

I want to upload a file to a ftp server programmatically (C++). If the connection is lost while uploading a file, I wouldn’t want to upload the file from scratch, but to upload only the part that I haven’t sent.

Does the APPE command fulfill my demand? What list of FTP commands should I use exactly? And how?

Answer 1

Check the RFC and specifically the APPEND command:

This
command causes the server-DTP to
accept the data transferred via the
data connection and to store the data
in a file at the server site. If the
file specified in the pathname exists
at the server site, then the data
shall be appended to that file;
otherwise the file specified in the
pathname shall be created at the
server site.

Note that you cannot simply APPEND the same file again. You should send the bytes remaining. That is, continue at the same position when the connection was lost.