On Mon, 8 May 2023 at 21:05, Jonathan Wakely wrote: > > > > On Mon, 8 May 2023, 20:00 Baribault, Carl via Gcc-help, <gcc-help@xxxxxxxxxxx> wrote: >> >> Dear Help, >> >> The subject identifier is nowhere defined. >> >> Please let me know if you need any more information. Thank you. > > > Yes, we need more info, you've provided none at all. > > That is a built-in function provided by the compiler, present since gcc 9.1.0 > > In what context are you seeing it not defined? What are you trying to do, and what error do you get? Here's the proof it is defined: https://godbolt.org/z/cWK7fzYxK Maybe you're trying to use it in C code instead of C++?