Re: More C type errors by default for GCC 14

[David Brown <david@westcontrol.com>]

On 12/05/2023 04:08, Po Lu via Gcc wrote:
> Eli Schwartz <eschwartz93@gmail.com> writes:
> 

>>
>> Because that's exactly what is going on here. Features that were valid
>> C89 code are being used in a GNU99 or GNU11 code file, despite that
>> ***not*** being valid GNU99 or GNU11 code.
> 
> How GCC currently behaves defines what is valid GNU C.
> 

What GCC /documents/ defines what is valid GNU C.  (Much of that is, of 
course, imported by reference from the ISO C standards, along with 
target-specific details such as ABI's.)

Anything you write that relies on undocumented behaviour may work by 
luck, not design, and you have no basis for expecting future versions of 
gcc, or any other compiler, to give the same lucky results.

Each version of a compiler is, in fact, a different compiler - that is 
how you should be viewing your tools.  The move between different 
versions of the same compiler is usually much smaller than moving 
between different compiler vendors, but you still look at the release 
notes, change notices, porting information, etc., before changing.  You 
still make considered decisions, and appropriate testing.  You still 
check your build systems and modify flags if needed.  And you do that 
even if you are confident that your code is solid with fully defined 
behaviour and conforming to modern C standards - you might have a bug 
somewhere, and the new compiler version might have a bug.


>> I am not dictating anything to you or anyone else in this paragraph,
>> though? All I said was that if one writes a c89 program and tells the
>> compiler that, then they will not even notice this entire discussion to
>> begin with.
>>
>> What, precisely, have I dictated?
> 
> That people who are writing GNU C code should be forced to rewrite their
> code in ANSI C, in order to make use of GNU C extensions to the 1999
> Standard.
> 

You are joking, right?  Surely no one can /still/ be under the 
misapprehension that anyone is proposing GCC stop accepting the old 
code?  All that is changing is the default behaviour, which will mean 
some people might have to use an extra flag or two in their build setup.

> 
>> However, it does appear that we are still stuck in confusion here,
>> because you think that GCC is no longer able to compile such code, when
>> in fact it is able to.
> 
> It won't, not by default.
> 

That's pretty much irrelevant.  People don't use gcc without flags.  The 
only thing that will change is which flags you need to use.

If you are not in a position to change the source code, and not in a 
position to change the build flags, then you are not in a position to 
change the compiler version.  (That's fine, of course - in my line of 
work, I almost never change compiler version for existing projects.  I 
have old code where the makefile specifies gcc 2.95.)

David