[CMake] C++11 flag not being added

Roman Wüger roman.wueger at gmx.at
Fri Oct 16 15:21:00 EDT 2015 

You can use CMake 3.x on older systems. Write platform checks for specific C++11 features and implement "old" style code if the C++11 features (e.g. lambdas) are not available.

Use https://cmake.org/cmake/help/v3.1/prop_gbl/CMAKE_CXX_KNOWN_FEATURES.html and https://cmake.org/cmake/help/v3.1/module/WriteCompilerDetectionHeader.html?highlight=compiler%20detection%20header#module:WriteCompilerDetectionHeader to detect if your compiler supports your implementation.

Best Regards


> Am 16.10.2015 um 14:09 schrieb Hendrik Sattler <post at hendrik-sattler.de>:
> 
> 
> 
> Am 16. Oktober 2015 13:38:27 MESZ, schrieb Petr Bena <benapetr at gmail.com>:
>> By stable you mean Jessie that was recently released and is almost
>> nowhere in production yet? :)
>> 
>> On my debian server:
>> 
>> $ cmake --version
>> cmake version 2.8.9
>> 
>> On one of wikimedia's ubuntu servers (the newer ones):
>> 
>> $ cmake --version
>> cmake version 2.8.12.2
>> 
>> On travis-ci cmake is about 2.8.7 and on ubuntu PPA builder it's
>> probably same.
>> 
>> And we aren't even talking about 3.0, but 3.1 or newer. One would need
>> to be truly naive to expect newer version on some stable production
>> systems, that usually run well established older software (eg.
>> majority of them do).
>> 
>> On my dev PC I have last CMake of course, but I need to be able to
>> compile on other systems as well :)
>> 
>> This code is meant to be cross-platform and buildable on most of
>> supported OS'es, even on older versions. I sincerely hate programs
>> that requires extremely latest versions of tools or libraries for them
>> to work, because these are usually hard to build.
> 
> They want to self-compile the latest of your software but use several years old versions of everything else?
> I'd understand the Ubuntu use case but not the Debian oldstable one. 
> 
> If everyone develops like this, the software system grinds to a halt. Recursively, I mean.
> 
> Just as a reminder for you regarding people of other systems: using C++11 excludes a lot of older compilers, e.g. MS VS6 or 7.1 or 8 or 9 ;-)
> 
> OTOH, if you have a very specific target audience...
> 
>> On Fri, Oct 16, 2015 at 11:56 AM, Hendrik Sattler
>> <post at hendrik-sattler.de> wrote:
>>> 
>>> 
>>> Am 16. Oktober 2015 11:29:48 MESZ, schrieb Petr Bena
>> <benapetr at gmail.com>:
>>>> I think you completely misunderstood me. I know I can install it on
>> my
>>>> machine, but I can hardly install it on PC's or servers of users who
>>>> use my program.
>>>> 
>>>> I want to make it as easy as possible to let users compile my
>> program.
>>>> Having to install anything by hand instead of system package manager
>>>> is a big overhead to majority of users. CMake 3x is too new, it's
>>> 
>>> 
>>> Hey, 3.0.2 is even available in Debian stable, and that really says
>> something about older versions!
>>> 
>>> 
>>>> available by default almost nowhere, meaning this option is not
>>>> available to me at this time. Maybe in few years the situation will
>>>> change, but for now I will resort to that hack which works on older
>>>> versions that are generally available everywhere.
>>>> 
>>>> On Fri, Oct 16, 2015 at 11:26 AM, Pau Garcia i Quiles
>>>> <pgquiles at elpauer.org> wrote:
>>>>> Hello,
>>>>> 
>>>>> CMake 3.3.1 is available from my PPA, in case it helps:
>>>>> 
>>>>> https://launchpad.net/~pgquiles/+archive/ubuntu/ppa
>>>>> 
>>>>> 
>>>>> 
>>>>> On Fri, Oct 16, 2015 at 10:58 AM, Petr Bena <benapetr at gmail.com>
>>>> wrote:
>>>>>> 
>>>>>> If I did that nearly nobody would be able to compile my program as
>>>>>> cmake >= 3.1 is extremely rare on most distributions. Even
>> ubuntu's
>>>>>> PPA builder has some ancient version.
>>>>>> 
>>>>>> On Fri, Oct 16, 2015 at 9:44 AM, Petr Kmoch <petr.kmoch at gmail.com>
>>>> wrote:
>>>>>>> Hi Petr.
>>>>>>> 
>>>>>>> You're using a feature (`CMAKE_CXX_STANDARD`) introduced in
>> CMake
>>>>>>> version
>>>>>>> 3.1, so you should require a minimum version >= that.
>>>>>>> 
>>>>>>> You can learn the version of CMake by running `cmake --version`
>>>>>>> 
>>>>>>> Petr
>>>>>>> 
>>>>>>> On Thu, Oct 15, 2015 at 5:45 PM, Petr Bena <benapetr at gmail.com>
>>>> wrote:
>>>>>>>> 
>>>>>>>> What do you mean by "target" property? I don't see any target
>>>>>>>> mentioned there. I don't have this line in there. I don't know
>>>> which
>>>>>>>> CMake this is, it failed on server we use for unit tests, but I
>>>> have
>>>>>>>> required min. version set to 2.8.7
>>>>>>>> 
>>>>>>>> 
>>>>>>>> 
>>>>>>>> On Thu, Oct 15, 2015 at 5:41 PM, Matthew S Wallace
>>>>>>>> <mwallace at ccmtrading.com> wrote:
>>>>>>>>> What version of CMake are you using?  I’m using 3.3.2.  The
>>>> only
>>>>>>>>> other
>>>>>>>>> thing I did was:
>>>>>>>>> 
>>>>>>>>> set_property(GLOBAL PROPERTY CXX_STANDARD_REQUIRED)
>>>>>>>>> 
>>>>>>>>> I’m guessing this probably does nothing since it is probably
>> a
>>>> target
>>>>>>>>> property.
>>>>>>>>> 
>>>>>>>>> -Matt
>>>>>>>>> 
>>>>>>>>>> On Oct 15, 2015, at 10:34 AM, Petr Bena <benapetr at gmail.com>
>>>> wrote:
>>>>>>>>>> 
>>>>>>>>>> Can you elaborate on it a bit?
>>>>>>>>>> 
>>>>>>>>>> I put set(CMAKE_CXX_STANDARD 11) as first line of my
>>>> CMakeLists and
>>>>>>>>>> it
>>>>>>>>>> still doesn't work, without the hack I used I get errors
>> while
>>>>>>>>>> compiling.
>>>>>>>>>> 
>>>>>>>>>> Can you give me example file in which it works? I guess
>> there
>>>> is
>>>>>>>>>> more
>>>>>>>>>> needed for it to work.
>>>>>>>>>> 
>>>>>>>>>> On Tue, Oct 13, 2015 at 7:12 PM, Matthew S Wallace
>>>>>>>>>> <mwallace at ccmtrading.com> wrote:
>>>>>>>>>>> Thanks, setting the global variable solved my issue.
>>>>>>>>>>> 
>>>>>>>>>>> -Matt
>>>>>>>>>>> 
>>>>>>>>>>>> On Oct 13, 2015, at 10:46 AM, Johannes Zarl-Zierl
>>>>>>>>>>>> <johannes.zarl-zierl at jku.at> wrote:
>>>>>>>>>>>> 
>>>>>>>>>>>> Hi,
>>>>>>>>>>>> 
>>>>>>>>>>>> CXX_STANDARD is a target property, not a global one. You
>> can
>>>>>>>>>>>> either
>>>>>>>>>>>> set
>>>>>>>>>>>> CXX_STANDARD for every target that needs it, or set it
>>>> globally by
>>>>>>>>>>>> changing
>>>>>>>>>>>> the default value.
>>>>>>>>>>>> 
>>>>>>>>>>>> You can do the latter by setting the variable
>>>> CMAKE_CXX_STANDARD
>>>>>>>>>>>> before
>>>>>>>>>>>> defining any target that depends on it:
>>>>>>>>>>>> 
>>>>>>>>>>>> set(CMAKE_CXX_STANDARD 11)
>>>>>>>>>>>> 
>>>>>>>>>>>> HTH,
>>>>>>>>>>>> Johannes
>>>>>>>>>>>> 
>>>>>>>>>>>> On Tuesday 13 October 2015 10:22:36 Matthew S Wallace
>> wrote:
>>>>>>>>>>>>> I have the following two lines in my CMakeLists.txt
>>>>>>>>>>>>> 
>>>>>>>>>>>>> set_property(GLOBAL PROPERTY CXX_STANDARD 11)
>>>>>>>>>>>>> set_property(GLOBAL PROPERTY CXX_STANDARD_REQUIRED)
>>>>>>>>>>>>> 
>>>>>>>>>>>>> However when compiling some of my source files, the
>>>> -std=c++11
>>>>>>>>>>>>> flag
>>>>>>>>>>>>> is not
>>>>>>>>>>>>> added.
>>>>>>>>>>>>> 
>>>>>>>>>>>>> Just for good measure I added:
>>>>>>>>>>>>> target_compile_features(my_target PRIVATE
>> cxx_strong_enums)
>>>> to
>>>>>>>>>>>>> the
>>>>>>>>>>>>> target
>>>>>>>>>>>>> that was having the problem.
>>>>>>>>>>>>> 
>>>>>>>>>>>>> Not sure if it matters, but in this case the compile
>> error
>>>> I’m
>>>>>>>>>>>>> getting is
>>>>>>>>>>>>> complaining because I’m referencing a fully scoped enum.
>>>> If I
>>>>>>>>>>>>> explicitly
>>>>>>>>>>>>> include -std=c++11 in my compile flags, everything works.
>>>>>>>>>>>>> 
>>>>>>>>>>>>> I’m thinking I’m probably just misunderstanding how
>>>> CXX_STANDARD
>>>>>>>>>>>>> works, but
>>>>>>>>>>>>> any help would be appreciated.
>>>>>>>>>>>>> 
>>>>>>>>>>>>> -Matt
>>>>>>>>>>>> 
>>>>>>>>>>>> --
>>>>>>>>>>>> 
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>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>> --
>>>>> Pau Garcia i Quiles
>>>>> http://www.elpauer.org
>>>>> (Due to my workload, I may need 10 days to answer)
>>>> --
>>>> 
>>>> Powered by www.kitware.com
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