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Q&A Is `-isystem` a POSIX cc option?

To use this StackExchange answer as a starting point, the latest POSIX standard does not specify a cc command at all: POSIX 1003.1-2001 (Single Unix v3) specifies c99 instead of c89, to use an u...

posted 2y ago by deleted user

Answer
#1: Initial revision by (deleted user) · 2022-04-25T11:35:58Z (almost 2 years ago)
To use [this StackExchange answer](https://unix.stackexchange.com/a/379452) as a starting point, the latest POSIX standard does not specify a `cc` command at all:

> POSIX 1003.1-2001 (Single Unix v3) specifies `c99` instead of `c89`, to use an updated standard dialect of C. You can see some editorial traces left from a draft that included a cc utility as well, but cc was removed from the specification. POSIX 1003.1-2008 (Single Unix v4) again just has `c99`

So you can't rely on the _existence_ of a `cc` command, much less its options.

If we look at what the [latest POSIX actually says](https://pubs.opengroup.org/onlinepubs/9699919799/utilities/c99.html) about the `c99` command, there is no reference to an `-isystem` option.

So I think the answer to your question is no. If you want to rely strictly on POSIX-mandated compiler options, you cannot use `-isystem`.