* How to best cope with variadic input
@ 2011-03-01 5:12 richardcavell
2011-03-01 8:59 ` Jonathan Wakely
0 siblings, 1 reply; 4+ messages in thread
From: richardcavell @ 2011-03-01 5:12 UTC (permalink / raw)
To: gcc-help
Hi everyone. I've decided to learn C99, and so I'm passing -std=c99 to
gcc. I've decided to write a Wikipedia bot in C (don't laugh).
Owing partly to obsessive tendencies and partly due to the need for the
bot to be robust in working unattended at high speed, I want to wrap
printf in a wrapper that automatically detects when printf has failed
and tells the user. The idea is that it is called like this:
int res = safeprint ( __FILE__ , __LINE__ , "Blah" ) ;
if ( res < 0 ) // uh oh
But printf has variadic input. I am scratching my head wondering what
is my best option:
1. Make safeprint a variadic function (I don't know how to do this)
2. Turn on C++ and overload safeprint with different combinations of
arguments
3. Create multiple safeprint functions with different names, that take
different combinations of arguments
Any advice for me? TIA.
-----------------------------------
#include <stdio.h>
#include <string.h>
#include "Error.h"
static const unsigned int StringMax = 100 ;
int safeprint ( const char* file , const unsigned int line , const
char* pstring )
{
int ilength = strlen ( pstring ) ;
int icharsprinted = printf ( "%s" , pstring ) ;
if ( ilength != icharsprinted )
{
Error ( file , line ) ;
return -1 ;
}
return 0 ;
}
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: How to best cope with variadic input
2011-03-01 5:12 How to best cope with variadic input richardcavell
@ 2011-03-01 8:59 ` Jonathan Wakely
2011-03-01 11:33 ` Maximilian Schneider
0 siblings, 1 reply; 4+ messages in thread
From: Jonathan Wakely @ 2011-03-01 8:59 UTC (permalink / raw)
To: richardcavell; +Cc: gcc-help
On 1 March 2011 05:11, <richardcavell@mail.com> wrote:
> Hi everyone. I've decided to learn C99, and so I'm passing -std=c99 to gcc.
> I've decided to write a Wikipedia bot in C (don't laugh).
>
> Owing partly to obsessive tendencies and partly due to the need for the bot
> to be robust in working unattended at high speed, I want to wrap printf in a
> wrapper that automatically detects when printf has failed and tells the
> user. The idea is that it is called like this:
>
> int res = safeprint ( __FILE__ , __LINE__ , "Blah" ) ;
> if ( res < 0 ) // uh oh
>
> But printf has variadic input. I am scratching my head wondering what is
> my best option:
>
> 1. Make safeprint a variadic function (I don't know how to do this)
Use va_list, va_start, va_arg and va_end, defined by:
#include <stdarg.h>
On GNU/Linux you should be able to say "man stdarg.h" to see usage examples.
> 2. Turn on C++ and overload safeprint with different combinations of
> arguments
A better option would be to use a C++ variadic template.
> 3. Create multiple safeprint functions with different names, that take
> different combinations of arguments
That would be inconvenient to use.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: How to best cope with variadic input
2011-03-01 8:59 ` Jonathan Wakely
@ 2011-03-01 11:33 ` Maximilian Schneider
2011-03-01 21:41 ` Jonathan Wakely
0 siblings, 1 reply; 4+ messages in thread
From: Maximilian Schneider @ 2011-03-01 11:33 UTC (permalink / raw)
To: richardcavell; +Cc: gcc-help
On Tue, 2011-03-01 at 08:59 +0000, Jonathan Wakely wrote:
> On 1 March 2011 05:11, <richardcavell@mail.com> wrote:
> > Hi everyone. I've decided to learn C99, and so I'm passing -std=c99 to gcc.
> > I've decided to write a Wikipedia bot in C (don't laugh).
> >
> > Owing partly to obsessive tendencies and partly due to the need for the bot
> > to be robust in working unattended at high speed, I want to wrap printf in a
> > wrapper that automatically detects when printf has failed and tells the
> > user. The idea is that it is called like this:
> >
> > int res = safeprint ( __FILE__ , __LINE__ , "Blah" ) ;
> > if ( res < 0 ) // uh oh
> >
> > But printf has variadic input. I am scratching my head wondering what is
> > my best option:
> >
> > 1. Make safeprint a variadic function (I don't know how to do this)
>
> Use va_list, va_start, va_arg and va_end, defined by:
> #include <stdarg.h>
>
> On GNU/Linux you should be able to say "man stdarg.h" to see usage examples.
>
> > 2. Turn on C++ and overload safeprint with different combinations of
> > arguments
>
> A better option would be to use a C++ variadic template.
>
> > 3. Create multiple safeprint functions with different names, that take
> > different combinations of arguments
>
> That would be inconvenient to use.
I would have to agree with Jonathan here. In my experience with c++ (Qt)
overloading has only caused me trouble.
the va_list method is straight forward. Note that printf() even comes in
a va_list compatible form. vprintf()
Max S.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: How to best cope with variadic input
2011-03-01 11:33 ` Maximilian Schneider
@ 2011-03-01 21:41 ` Jonathan Wakely
0 siblings, 0 replies; 4+ messages in thread
From: Jonathan Wakely @ 2011-03-01 21:41 UTC (permalink / raw)
To: Maximilian Schneider; +Cc: richardcavell, gcc-help
On 1 March 2011 11:33, Maximilian Schneider wrote:
> On Tue, 2011-03-01 at 08:59 +0000, Jonathan Wakely wrote:
>> > 2. Turn on C++ and overload safeprint with different combinations of
>> > arguments
>>
>> A better option would be to use a C++ variadic template.
[snip]
> I would have to agree with Jonathan here. In my experience with c++ (Qt)
> overloading has only caused me trouble.
I'm not sure we agree :)
I have no problem with using overloaded functions, but writing lots of
overloaded functions would be a headache. A single variadic template
would do a better job than an entire set of overloaded functions, see
the printf template at
http://www.generic-programming.org/~dgregor/cpp/variadic-templates.html
But I do agree that for this case, where the original code is in C,
simply using <stdarg.h> and vprintf is the most straightforward
solution.
^ permalink raw reply [flat|nested] 4+ messages in thread
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2011-03-01 5:12 How to best cope with variadic input richardcavell
2011-03-01 8:59 ` Jonathan Wakely
2011-03-01 11:33 ` Maximilian Schneider
2011-03-01 21:41 ` Jonathan Wakely
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