[Swan-dev] CentOS 6 "implicit declaration of function ‘printf’"

Andrew Cagney andrew.cagney at gmail.com
Tue Jun 18 20:04:52 UTC 2019

why is a library function calling printf()? (if a c file needs
something #include it).

On Tue, 18 Jun 2019 at 11:55, D. Hugh Redelmeier <hugh at mimosa.com> wrote:
> Sorry, I was addressing this subject before I read this message.
> On Tue, 18 Jun 2019, Antony Antony wrote:
> | From: Antony Antony <antony at phenome.org>
> | A while ago, while many of you  were busy pushing 3.28 release an annoying
> | warning/error crept in, travis test reported it only on CentOS 6. As I
> | recollect, it was discarded as not important on IRC. I thought I will drop
> | an e-mail about it.
> Yeah.  We're good at ignoring things in any medium.
> | The proposed fix is disable all warnings, WERROR_CFLAGS= for CentOS or older
> | compilers. I wonder if there is a better fix for it.
> For sure.  The "implicit declaration" warning message is one that we
> really need to treat as an error because it indicates a breakdown that
> will cause strong type-checking to be disabled.  Also, implicit
> declaration of a varargs function is just wrong.
> | And also curious what
> | triggered this, the commit is shuffling include files around. I could not
> | figure which line is causing warning.
> It a philosophy change :-)
> When I structured Pluto, I decided that certain headers were so
> pervasive that they could be #included in one central header,
> reducing the clutter in each individual source file.
> This guiding idea is gone.  I don't know what the replacement guiding
> idea is.
> After all, "printf" should mean the same thing wherever it is used.
> It is true that there are some places where it should not be used:
> not every context has stdout hooked up in a meaningful way.  I'm not
> sure that it is meaningful in lib/libswan/addr_lookup.c.
> In any case, #include <stdio.h> should be pervasively available
> (except for kernel code, I guess) so snprintf(3) is available.
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