Complete list of Clang flags

Question

Where can I find a complete list of Clang flags?

There are some, like -include-pch, that don't appear to be even listed in the man page. :(

I know that GCC uses some of the same flags, but it doesn't include documentation for stuff like -Os which I believe is only available in Clang. Is there a place where I can find a single, consolidated list of all the Clang options ever?

See [this answer by Chandler Carruth, clang developer](https://softwareengineering.stackexchange.com/questions/122608/clang-warning-flags-for-objective-c-development/124574#124574). — ShreevatsaR, Aug 09 '17 at 03:56
Version-dependent options: [Clang warning flags](https://github.com/barro/compiler-warnings#clang-warning-flags). Though it only lists the names of the options (not the documentation). — Peter Mortensen, Oct 25 '22 at 17:11

score 89 · Accepted Answer · edited Dec 31 '20 at 00:17

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I don't know if this is exactly what you want. Maybe more options are described elsewhere, but I think you are interested in the Clang frontend options. By default, the options displayed seem to describe the "GCC-compatible driver".

clang -cc1 --help should give you what you want.

edited Dec 31 '20 at 00:17

Peter Mortensen

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answered Oct 25 '11 at 19:21

Guillaume Papin

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Thanks, this is the best option I've seen so far. – Colen Oct 26 '11 at 22:00
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is there a way to list all possible warnings for `-W`? – marcin May 12 '13 at 21:22
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I don't think so. There is `-Weverything` if you want to activate all of them though. Since Clang tries to be compatible with GCC you can take a look at GCC's ones (`gcc --help=warnings`). – Guillaume Papin May 12 '13 at 21:52
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Some more info here http://programmers.stackexchange.com/a/124574 and here http://www.noxeos.com/2012/01/10/warning-flags-clang/. Note that `-Weverything` that I mentioned earlier is not for everyday use but more for 'experimentation'. – Guillaume Papin May 12 '13 at 22:03
@GuillaumePapin can you eleborate on what the '-cc1' option does? I can't find it documented anywhere – tjk213 Oct 28 '14 at 17:56
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You can see at the [Clang - FAQ](http://clang.llvm.org/docs/FAQ.html#i-run-clang-cc1-and-get-weird-errors-about-missing-headers) that `clang -cc1` is the frontend. `clang` is the GCC-compatible driver. And recently, a new driver has appeared, `clang-cl`, which is a CL-compatible driver. I don't know how to explain `clang -cc1` properly but the word that matters is **frontend**. You should get answers by looking for "compiler frontend", "clang frontend". – Guillaume Papin Oct 28 '14 at 23:55
How come none of these places document -shared or -dynamiclib? – Jake Oct 11 '19 at 02:26

score 8 · Answer 2 · edited Dec 31 '20 at 00:17

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There are many hidden options in LLVM:

clang --help-hidden
opt --help-hidden

edited Dec 31 '20 at 00:17

Peter Mortensen

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answered Mar 04 '19 at 07:48

DTharun

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score 7 · Answer 3 · answered Apr 25 '17 at 22:44

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For Clang, they are listed in the diagnostics reference, which can be found on the documentation website here

answered Apr 25 '17 at 22:44

Zoodle Von Noodleson

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Better: https://clang.llvm.org/docs/ClangCommandLineReference.html – Andrew Feb 14 '21 at 04:16
the command line reference only references -W but with the diagnostics reference page, you can find that it takes -Wdeprecated-objc-isa-usage, for example. – Jake Mar 07 '21 at 01:07

score 2 · Answer 4 · answered Dec 04 '22 at 17:05

If you want to get a complete list of warning flags, including hierarchies (IE which sub-flags are enabled by groups like -Wall), you can use the LLVM tool diagtool.

$ diagtool tree Will print the complete list of warnings clang supports.
$ diagtool tree -Wnon-gcc will print the warnings enabled by -Wnon-gcc.

The warnings are color-coded:

RED = it does nothing, exists only for GCC compatibility
GREEN = the warning is enabled by default
YELLOW = the flag enables new behavior

Finally, I wrote a short script if you're interested in viewing the diff between sets of flags (see image below)

For example: -Wall -> -Wall -Wextra ->-Wall -Wextra -Wnon-gcc:

Here is a set of flags not enabled by your typical -Wall -Wextra -Wpedantic for Clang (as of LLVM 16 dev) you might find useful, that I scraped from the output of diagtool:

https://gist.github.com/GavinRay97/bae1d93925e55ce0a0084946f24984cf

Hope someone out there finds this information useful =)

Complete list of Clang flags

4 Answers4

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