[dgrunwald]

What's being removed in C23 is the ancient K&R syntax for function definitions:

    int max(a, b)
    int a, b;
    {
        return a>b?a:b;
    }

My understanding is that C23 does not change the meaning of function declarations. So "void foo();" remains a declaration of a function accepting an unknown number of parameters.

[mojuba]

According to the OP tweet though, `foo()` is now a function that takes no arguments.

[zx2c4]

Here's the document for that change: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2841.htm

> In this proposal, a function declarator without a parameter list declares a prototype for a function that takes no parameters (like it does in C++).

And it seems like gcc implements this under -std=c2x now:

    zx2c4@thinkpad /tmp $ cat a.c
    int blah()
    {
            return 7;
    }
    
    int main(int argc, char *argv[])
    {
            return blah(argc);
    }
    zx2c4@thinkpad /tmp $ gcc -std=c17 a.c
    zx2c4@thinkpad /tmp $ gcc -std=c2x a.c
    a.c: In function ‘main’:
    a.c:8:16: error: too many arguments to function ‘blah’
        8 |         return blah(argc);
          |                ^~~~
    a.c:1:5: note: declared here
        1 | int blah()
          |     ^~~~

[leetrout]

Agree the tweet makes it seem the behavior is changing.

Edit: parent is correct it IS changing

> We could make this change because foo() decls and definitions had been deprecated since C89/99, longer than I've been alive.

> Implementations will likely warn on foo() decls for a while, and error if someone calls it with foo(too, many, args);.

https://mobile.twitter.com/__phantomderp/status/149481259506...

[jesprenj]

Wouldn't int foo(void) be a function that takes no arguments and int foo() a function that takes an unknown number of arguments?

[suprjami]

Yes, that's the problem.

[duskwuff]

Which is much more consistent, IMO.

int foo(int, int) is a function taking two arguments. int foo(int) is a function taking one argument. int foo() ought to mean a function taking no arguments, not a function with an unspecified number of arguments!

[suprjami]

That's a different thing. That's implied `foo(void)`.

[messe]

It WAS a different thing. That's changing in C23.

[josephcsible]

I'm particularly unhappy that K&R declarations are going away without https://www9.open-std.org/JTC1/SC22/WG14/www/docs/n2780.pdf being added to replace them. Now there's some functions that you can't write anymore.

[zh3]

Wow, that's annoying. There's a bunch of old code we have that'll need updating (written that way to keep the line lengths down).

[MawKKe]

...can't you just configure your build system to compile those modules with pre-c23 standard?

[zh3]

Of course. But one of the great things about C is that as a rule nothing breaks with compiler changes (as long as appropriate care has been taken) which this appears to violate.

[klyrs]

All the compilers I use have a default C version, and an optional flag to control which version to use. It's a non-issue.

[rightbyte]

Maybe the compiler will add a extension flag? I mean the K&R declarations still need to be supported in the compiler for earlier standards.