[llvm-dev] LLVM coding standards and order of includes

[David Blaikie via llvm-dev]

On Thu, Sep 10, 2015 at 9:00 AM, Martin J. O'Riordan <
martin.oriordan at movidius.com> wrote:

> Generally it is safer to include ISO headers first (using the ‘#include
> <...>’ form) so as to minimise the possibility that a later user
> declaration or macro definition interferes with the correctness of the
> Standard libraries.  It also tends to make pre-compiled header
> implementations faster and more shareable across a larger set of files.
>

As a complete aside, I'm curious which implementation of precompiled
headers you're referring to. The only one I'm familiar with is MSVC's which
requires a designated PCH that must be first, not just earlier. Generally
we won't put a system header first, we'll put the corresponding .h for this
.cpp file first - as a way to test that that header is standalone (ie:
doesn't depend on any other inclusions before it)

(& FWIW Clang's modules support is a more general form of PCH that doesn't
have these limitations - C++ support is ongoing, though)


>
>
> I would like to suggest revising the LLVM coding standard to place the “
> System #includes” first.
>
>
>
>             MartinO
>
>
>
> *From:* llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] *On Behalf Of *David
> Blaikie via llvm-dev
> *Sent:* 10 September 2015 16:33
> *To:* Russell Wallace <russell.wallace at gmail.com>
> *Cc:* llvm-dev <llvm-dev at lists.llvm.org>
> *Subject:* Re: [llvm-dev] LLVM coding standards and order of includes
>
>
>
>
>
>
>
> On Thu, Sep 10, 2015 at 8:06 AM, Russell Wallace via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
> According to the LLVM coding standards,
>
>
>
> Immediately after the header file comment
> <http://llvm.org/docs/CodingStandards.html#header-file-comment> (and
> include guards if working on a header file), the minimal list of #includes
> <http://llvm.org/docs/CodingStandards.html#minimal-list-of-includes>required
> by the file should be listed. We prefer these #includes to be listed in
> this order:
>
>    1. Main Module Header
>    2. Local/Private Headers
>    3. llvm/...
>    4. System #includes
>
> If a program is using LLVM, and also using a third-party library such as
> GMP, where would the coding standard have the GMP include be placed
> relative to the above order?
>
>
> The LLVM coding conventions are really intended for LLVM's code itself,
> they probably don't cover many situations that would arise when using LLVM
> code in broader applications like this... (nor is it likely we'd want to
> add wording to the style guide to clarify those use cases, unfortunately).
>
> That said, we do have one (zlib compression?) or two (maybe md5 too?)
> external libraries used in LLVM, I imagine they get bundled in with the
> system includes, but I've not looked (& given that there aren't many, they
> might not be done in any consistent/deliberate manner)
>
> - Dave
>
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