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From: Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: printf and time_t
Date: Thu, 05 Feb 2026 21:10:57 -0800
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Bart <bc@freeuk.com> writes:
[...]
> /Some/ compilers with /some/ options will /sometimes/ tell you when
> you've got it wrong.
>
> But you first have to make an educated guess, or put in some dummy
> format code.
>
> Eventually, it will compile. Until someone else builds your program,
> using a slightly different set of headers where certain types are
> defined, and then it might either give compiler messages that they
> have to fix, or it show wrong results.

That's not how I do it, and I don't think it's how most programmers do
it.

I know the rules well enough that I can usually write a correct format
string in the first place.  If I make a mistake, gcc's warnings are a
nice check.

> If I compile this code with 'gcc -Wall -Wextra -Wpedantic':
>
>   #include <stdio.h>
>
>   int main() {
>       int a = -1;
>       printf("%u", a);
>   }
>
> it says nothing. The program displays 4294967295 instead of -1.

The behavior is unsurprising.  The lack of a warning is very mildly
inconvenient.

> If compile this version (using %v) using a special extension:
>
>   #include <stdio.h>
>
>   int main() {
>       int a = -1;
>       printf("%v", a);
>   }
>
> it shows -1. Which is better?

The one I can actually use.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */