We have tried BOTH ways (on Sequoia/arm64): without lldb, that is "serveur.out" with lldb, that is "lldb server.out" Most of the post shows the second call (with lldb). We are NOT creating an "app" (in the macOS sense) at the moment. We start our programs from the Terminal (Serveur on 1 window, Client on another window, both in the same machine or not -- communication is done by sockets) ==> Since then, we have tried to change from clang to another C++ compiler. Still problems with gcc The problem disappears with c++ ! We are now sure that the problem comes from the amr64 version of clang, because exactly the same code runs without problems on Sequoia/x86_64/clang.