gcc default standard

gcc default standard

[Mehdi Megherbi]

Hi

I'm using ubuntu 20.04 and his default gcc version (9.3.0), with standard C++14 as default. I have to compile from source a lot of scientific toolkits, all made with C++11. After a lot of research I was not able to find a way to select the default standard of g++/gcc, so cmake/make take by default the wrong standard and I get always crashs. There is really no intrensec way to select the default standard used ? cmake projects sometimes add an option to select the standard for compilation but unfortunetly not all projects

Regards
Mehdi

Re: gcc default standard

[Jonathan Wakely]

On Fri, 11 Jun 2021 at 10:17, Mehdi Megherbi via Gcc-help
<gcc-help@gcc.gnu.org> wrote:
>
> Hi
>
> I'm using ubuntu 20.04 and his default gcc version (9.3.0), with standard C++14 as default. I have to compile from source a lot of scientific toolkits, all made with C++11. After a lot of research I was not able to find a way to select the default standard of g++/gcc, so cmake/make take by default the wrong standard and I get always crashs.

Crashes? What is crashing? The toolkits you're compiling? GCC? Cmake?
Do you just mean it doesn't compile, or is it compiling and then
crashing when you run the software?

Most C++11 code will compile without problems using -std=gnu++14, so
I'm not sure what the problem is.


>There is really no intrensec way to select the default standard used ?

No.

Some makefiles will respect the CXXFLAGS variable, but not all.

A brute force solution would be to create a wrapper script around gcc
and g++ which always adds your preferred -std option and put that
script earlier in your PATH than the real gcc executables:

#!/bin/sh
exec g++ "$@" -std=gnu++11

Re: gcc default standard

[Mehdi Megherbi]

> On Fri, 11 Jun 2021 at 10:17, Mehdi Megherbi via Gcc-help <gcc-help@gcc.gnu.org<mailto:gcc-help@gcc.gnu.org>> wrote:

> >

> > Hi

> >

> > I'm using ubuntu 20.04 and his default gcc version (9.3.0), with standard C++14 as default. I have to compile from source a lot of scientific toolkits, all made with C++11. After a lot of research I was not able to find a way to select the default standard of g++/gcc, so cmake/make take by default the wrong standard and I get always crashs.

>

> Crashes? What is crashing? The toolkits you're compiling? GCC? Cmake?

> Do you just mean it doesn't compile, or is it compiling and then crashing when you run the software?

>

> Most C++11 code will compile without problems using -std=gnu++14, so I'm not sure what the problem is.

>

> >>sorry for not getting more informations, for example with ROOT cern

> >>toolkit, if you let C++14 it will switch to the beta version of

> >>ROOT. And Geant4 toolkit also, it creates a lot warnings during

> >>compilation. Another decisive exemple is NPTOOL, it simply crash

> >>during compilation, because of the standard

>

>

> >There is really no intrensec way to select the default standard used ?

>

> No.

>

> Some makefiles will respect the CXXFLAGS variable, but not all.

>

> A brute force solution would be to create a wrapper script around gcc and g++ which always adds your preferred -std option and put that script earlier in your PATH than the real gcc executables:

>

> #!/bin/sh

> exec g++ "$@" -std=gnu++11

>

> >> I'm suposed to write this in .sh file and source it ?

Re: gcc default standard

[Jonathan Wakely]

On Fri, 11 Jun 2021, 21:31 Mehdi Megherbi via Gcc-help, <
gcc-help@gcc.gnu.org> wrote:

> > On Fri, 11 Jun 2021 at 10:17, Mehdi Megherbi via Gcc-help <
> gcc-help@gcc.gnu.org<mailto:gcc-help@gcc.gnu.org>> wrote:
>
> > >
>
> > > Hi
>
> > >
>
> > > I'm using ubuntu 20.04 and his default gcc version (9.3.0), with
> standard C++14 as default. I have to compile from source a lot of
> scientific toolkits, all made with C++11. After a lot of research I was not
> able to find a way to select the default standard of g++/gcc, so cmake/make
> take by default the wrong standard and I get always crashs.
>
> >
>
> > Crashes? What is crashing? The toolkits you're compiling? GCC? Cmake?
>
> > Do you just mean it doesn't compile, or is it compiling and then
> crashing when you run the software?
>
> >
>
> > Most C++11 code will compile without problems using -std=gnu++14, so I'm
> not sure what the problem is.
>
> >
>
> > >>sorry for not getting more informations, for example with ROOT cern
>
> > >>toolkit, if you let C++14 it will switch to the beta version of
>
> > >>ROOT. And Geant4 toolkit also, it creates a lot warnings during
>
> > >>compilation. Another decisive exemple is NPTOOL, it simply crash
>
> > >>during compilation, because of the standard



So you really mean crash? Or just fails to compile?

What errors do you get?




> > >There is really no intrensec way to select the default standard used ?
>
> >
>
> > No.
>
> >
>
> > Some makefiles will respect the CXXFLAGS variable, but not all.
>
> >
>
> > A brute force solution would be to create a wrapper script around gcc
> and g++ which always adds your preferred -std option and put that script
> earlier in your PATH than the real gcc executables:
>
> >
>
> > #!/bin/sh
>
> > exec g++ "$@" -std=gnu++11
>
> >
>
> > >> I'm suposed to write this in .sh file and source it
>


No, put it in a file called g++ and make it executable, and use that
instead of the real g++ file. That will run the compiler with -std=gnu++11