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I'm programming on a c project and use code from another author. I change the main functionality to a new, complete other one. The most of the new code is my own but some files are untouched and others are modified.

Every file of the other author begins like this:

/*
* Copyright (C) 2005 - authors name <authors_name@hotmail.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
*/

1) Could I use GPL V3 and my own copyright for the main project (with or without naming the other author)?

2) How should be the header of files with fewer changes (like adding little functions and rename classes)?

3) One file is the original without changes. Should I left it as it is or should I update the GPL to V3 and add my copyright (with or without deleting the other authors name)?

  • 1
    You can't claim copyright on this code, regardless of which license is already on it. – Robert Harvey Aug 21 '16 at 18:55
3

The original owner is the copyright owner, GPL or not. Replacing his copyright notice with your own means you are making a fraudulent claim that you are the copyright owner. Apart from that it's a bloody cheek.

2

1) Could I use GPL V3 and my own copyright for the main project (with or without naming the other author)?

The copyright notice must include the other author, because they still have copyright over (part of the) work. The GPL license specifies that it must apply to any derived work, sou you must use GPL-3.0. You may chose to license the sources you wrote yourself under more permissive license, but any compiled binaries have to be GPL-3.0.

2) How should be the header of files with fewer changes (like adding little functions and rename classes)?

You should add yourself to the copyright line. You must keep the original author listed and you must keep the license, because the license requires it.

3) One file is the original without changes. Should I left it as it is or should I update the GPL to V3 and add my copyright (with or without deleting the other authors name)?

You may add yourself, but you must not remove the original author and may not change the license.

A GPL-3.0 project may contain sources with more permissive licenses that can be sublicensed to GPL-3.0 like MIT or GPL-2.0+ (but not GPL-2.0!). That license applies to those sources only. You can upgrade them when you modify them if you wish. In either case, you need to clearly state the project as a whole is covered by GPL-3.0.

  • GPL v2 for question 2) and 3) or could I update all to GPL v3? – C-Jay Aug 22 '16 at 15:29
  • @C-Jay: No. GPL-2.0 can't be upgraded. Fortunately, most software (Linux (Linux is only the kernel) being notable exception) is under GPL-2.0+, that is "GPL version 2 or, at your option, any later version", and that can be upgraded, because it is explicitly permitted. – Jan Hudec Aug 22 '16 at 18:37

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