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Re: Mandates explicit -std=c++XY for c++ projects




Ansgar,

On Tue, Oct 10, 2017 at 9:17 AM, Mathieu Malaterre <malat@xxxxxxxxxx> wrote:
> Ansgar,
>
> On Tue, Oct 10, 2017 at 9:11 AM, Ansgar Burchardt <ansgar@xxxxxxxxxx> wrote:
>> Mathieu Malaterre writes:
>>> With this mind I'd like to make mandatory the -std=c++XY flags when
>>> compiling either a c++ library or a stand-alone c++ program:
>>>
>>> 1. Either upstream define the explicit -std=c++XY flags by mean of its
>>> build system,
>>> 2. Or the package maintainers needs to explicit change the CXXFLAGS to
>>> pass the appropriate version of the c++ standard. In which case this
>>> should be documented in the README.Debian file.
>>> 3. As a fallback, dh should initialize the CXXFLAGS with -std=gnu++98
>>
>> So if the upstream build system adds '-std=c++14' and CXXFLAGS is set to
>> '-std=gnu++98', one gets '-std=c++14 -std=gnu++98' and building the
>> package no longer works?  That doesn't sound good to me.
>
> My bad, I assumed this would be the opposite, just like the -O3 vs
> -O2, so the latest flags would be considered. Let me double check with
> a cmake package.

So I verified with a CMake package where:

$ cat CMakeLists.txt
[...]
set(CMAKE_CXX_STANDARD 98)

I have then set:

$ cat debian/rules
[...]
export DEB_CXXFLAGS_MAINT_APPEND = -std=c++14

This leads:

cd /tmp/gdcm-2.8.2/obj-x86_64-linux-gnu/Source/Common && /usr/bin/c++
 -DgdcmCommon_EXPORTS
-I/tmp/gdcm-2.8.2/obj-x86_64-linux-gnu/Source/Common
-I/tmp/gdcm-2.8.2/Source/Common
-I/tmp/gdcm-2.8.2/Source/DataStructureAndEncodingDefinition
-I/tmp/gdcm-2.8.2/obj-x86_64-linux-gnu/Testing/Source/Data
-I/tmp/gdcm-2.8.2/Testing/Source/Data -I/tmp/gdcm-2.8.2/Utilities  -g
-O2 -fdebug-prefix-map=/tmp/gdcm-2.8.2=. -fstack-protector-strong
-Wformat -Werror=format-security -std=c++14 -Wdate-time
-D_FORTIFY_SOURCE=2 -fPIC   -std=gnu++98 -o
CMakeFiles/gdcmCommon.dir/gdcmBoxRegion.cxx.o -c
/tmp/gdcm-2.8.2/Source/Common/gdcmBoxRegion.cxx

So the upstream flag -std=gnu++98 (since it comes last) is properly considered.

Was this the setup you had in mind ?

Thanks for your comments,