Who is "we"? I'm a UNIX/C programmer for decades and I don't care about this. There is no such thing as beautiful API design. Every design is a compromise. If

Who is "we"? I'm a UNIX/C programmer for decades and I don't care about this. There is no such thing as beautiful API design. Every design is a compromise. If you think non-reentrant calls should be deprecated in POSIX take it to the committee. There is a myriad of non-reentrant code both in POSIX spec and in libc implemenations. You need to RTFM, I'm sorry. There is no "coherent API" as far as null termination goes too. Some library functions deal with it, some calls don't. You need to RTFM. I also want to know OP's reason to even use setenv() in a multithreaded piece of software. It's like an oxymoron. setenv and vars are useful to pass on data from parent process to forked children because they inherit the environment. If you use the threading model you don't need it. If your application is a single process setenv() is useless.