7-Zip is free software with open source. The most of the code is under the GNU LGPL license. Some parts of the code are under the BSD 3-clause License. Also ...
BSD 3-clause License is used for the code in 7z.dll that implements LZFSE data decompression. That code was derived from the code in the LZFSE compression ...
Yes, but you are required to specify in your documentation (1) that you used parts of the 7-Zip program, (2) that 7-Zip is licensed under the GNU LGPL license ...
7z-cpp Modifications placed under MIT The MIT License (MIT) Copyright (c) Jan Kaniewski (Getnamo), Keith J. Jones (keithjjones), Pavel Abakanov (KocourKuba) ...