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Re: A printf question.

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On 14/10/2015 04:55, glen herrmannsfeldt wrote:

> James Kuyper <jameskuyper@verizon.net> wrote:
> 
> (snip on printf with one argument)
> 
>> <stdio.h> brings in a prototype declaration of printf() like the following:
>>  
>> int printf(const char * restrict format, ...); (7.21.6.3p1)
>>  
>> Such a prototype requires that:
>> 1. The function be called with at least one argument.
>> printf(message) meets that requirement
>> 2. The type of that argument must be convertible to "const char*".
>> The type of message is "const char*", and therefore trivially convertible.
> 
> With compilers generating more and more warnings, possibly for things
> that are actually correct, I would not be surprised to see a warning
> for a single non-constant argument.

And it is indeed possible to request such a warning from gcc:
(Though it wouldn't fire in the OP's example)

> -Wformat-security: If -Wformat is specified, also warn about uses of
> format functions that represent possible security problems. At
> present, this warns about calls to printf and scanf functions where
> the format string is not a string literal and there are no format
> arguments, as in printf(foo). This may be a security hole if the
> format string came from untrusted input and contains ‘%n’. (This is
> currently a subset of what -Wformat-nonliteral warns about, but in
> future warnings may be added to -Wformat-security that are not
> included in -Wformat-nonliteral.)

https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html

Regards.

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A printf question. MehdiAmini <atorrses@gmail.com> - 2015-10-13 14:09 +0000
  Re: A printf question. Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-10-13 10:46 -0400
  Re: A printf question. Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-10-13 09:19 -0700
    Re: A printf question. Keith Thompson <kst-u@mib.org> - 2015-10-13 10:45 -0700
      Re: A printf question. David Brown <david.brown@hesbynett.no> - 2015-10-13 23:15 +0200
  Re: A printf question. James Kuyper <jameskuyper@verizon.net> - 2015-10-13 15:25 -0400
    Re: A printf question. glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-14 02:55 +0000
      Re: A printf question. James Kuyper <jameskuyper@verizon.net> - 2015-10-13 23:12 -0400
        Re: A printf question. supercat@casperkitty.com - 2015-10-14 06:34 -0700
          Re: A printf question. Keith Thompson <kst-u@mib.org> - 2015-10-14 10:26 -0700
        Re: A printf question. MehdiAmini <atorrses@gmail.com> - 2015-10-15 14:06 +0000
          Re: A printf question. James Kuyper <jameskuyper@verizon.net> - 2015-10-15 10:26 -0400
      Re: A printf question. Noob <root@127.0.0.1> - 2015-10-25 23:02 +0100

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