Moving the kernel to modern C [LWN.net]

Moving the kernel to modern C

Posted Feb 25, 2022 16:51 UTC (Fri) by Wol (subscriber, #4433)
In reply to: Moving the kernel to modern C by wtarreau
Parent article: Moving the kernel to modern C

I thought that was allowed in ancient C ...

Unless you mean actually declaring inside the "if" statement ... but I thought declaring after a { was permitted anywhere. I dunno, it's ages since I've programmed C in anger.

But it would be nice to say you can ONLY declare after a {, but that includes things like "int i = 1". You shouldn't be able to do things like "int i; i=1; int j; j=2;", though.

Cheers,
Wol

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Moving the kernel to modern C

Posted Feb 25, 2022 18:44 UTC (Fri) by nybble41 (subscriber, #55106) [Link]

In C89 and GNU89 declarations must occur before statements within each block. C89 additional requires initializers to be compiler-time constants. However, it's not as if this equivalent GNU89 code is any easier to follow:

#include <stdio.h>
#include <unistd.h>

int blah(long x, int j)
{
    long i = x ? x : -1;
    int k = i;
    {
        int i;
        for (i = 1; i < j; i++) {
            k += i * 2;
            {
                char i = (k & 1) ? 'O' : 'E';
                {
                    int pid = getpid();
                    printf("i=%d j=%d pid=%d\n", i, j, pid);
                }
            }
        }
    }
    return k;
}

The real lessons here are "use meaningful names" and "avoid shadowing".