The code has, at https://github.com/kspalaiologos/bzip3/blob/bf2f0e02fd59f4c497d27ca65cabf170715baddf/src/main.c#L66 https://github.com/kspalaiologos/bzip3/blob

The code has, at https://github.com/kspalaiologos/bzip3/blob/bf2f0e02fd59f4c497d27ca65cabf170715baddf/src/main.c#L66 https://github.com/kspalaiologos/bzip3/blob/bf2f0e02fd59f4c4... : } else if (argv[i][1] == 'j') { workers = atoi(argv[i + 1]); i++; If the last argument is "-j6" then this will read past the end of the allocated argv strings and try to do atoi(NULL): % ./bzip3 -j3 < README.md Segmentation fault "-j6" is standard getopt() behavior, and the default expected behavior from Unix/POSIX systems.