[Nauty] nauty and Traces in modern C++

[Brendan McKay]

Hi Johann,

You need the macros, but you can adjust the meaning in some cases.

First, make sure your code is reading the correct nauty.h.

The meaning of NORET_ATTR is chosen by the configure script.  In the case
of a modern C compiler (*), it will be defined as _Noreturn which is a 
function
attribute specifying that the function never returns (in this case 
because it
always calls exit()).  It helps optimization.

My guess is that your C++ compiler doesn't understand _Noreturn, so the 
declaration
of gt_abort is deemed invalid and then everything that uses gt_abort is
rejected as well; DYNALLOC1 in this case.

You can try selecting a more recent C++ version in your build instructions.

If all else fails, find this line in nauty-h.in:
     #define NORET_ATTR @ac_cv_noret@
and replace if by:
     #define NORET_ATTR
Then run ./configure again.  Lots of people use nauty in C++, though I am
not one of them.

I can modify the code to disable _Noreturn in the event of C++ compilation,
but if anyone else has suggestions about this I'd like to hear them.

Brendan.

(*) I read on the web that _Noreturn was introduced in C11, but it is 
present in
my copy of the C99 standard. Was it dropped at the last minute, perhaps?



On 10/2/2024 11:01 am, Johann Birnick via Nauty wrote:
> Hello,
>
> I want to use nauty and Traces in a modern C++ project, which uses 
> CMake for building. How to do that appropriately? In particular:
>
> 1. In my current setup, when I want to run an example from the
>    documentation, I get the following error:
>
>    /usr/include/nauty/gtools.h:302:24: error: expected initializer
>    before ‘gt_abort’
>       302 | extern void NORET_ATTR gt_abort(const char*);
>           |                        ^~~~~~~~
>    /home/johann/Coding/MabreSolve/main.cpp: In function ‘int main()’:
>    /home/johann/Coding/MabreSolve/main.cpp:31:13: error: ‘gt_abort’ was
>    not declared in this scope; did you mean ‘gt_abort_1’?
>        31 |             DYNALLOC1(int, lab1, lab1_sz, n, "malloc");
>           |             ^~~~~~~~~
>
>    Do you have any idea what's the problem and how to fix it?
>
> 2. I guess in modern C++ one shouldn't use all these in capital letters
>    written macros and global variables (DYNALLOC1, SG_ALLOC,
>    NAUTYVERSIONID, and so on). Is there a way to do this the 'modern 
> way'?
>
> Thank you very much in advance!
>
> Johann B.
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