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Is `-isystem` a POSIX cc option?

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Is -isystem/path/to/sys/includes a standard compiler option, or is it a compiler extension implemented by gcc, clang, and maybe other compilers? Can I rely on its availability?

I couldn't find the POSIX specification for cc(1).

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No, you cannot rely on its availability... (3 comments)

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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 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 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.

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