Re: [Caml-list] precision not working properly for strings in Printf?

From: Jonathan Bryant <jtbryant@valdosta.edu>
To: "Quôc Peyrot" <chojin@lrde.epita.fr>
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] precision not working properly for strings in Printf?
Date: Wed, 27 Jun 2007 00:11:01 -0400	[thread overview]
Message-ID: <8503CBAB-EF9E-4CF0-89A8-2F6E454CF4DC@valdosta.edu> (raw)
In-Reply-To: <86507DD0-1BCB-4BF9-A058-0809022E564C@lrde.epita.fr>

On Jun 26, 2007, at 11:48 PM, Quôc Peyrot wrote:

>
> On Jun 27, 2007, at 5:38 AM, Jonathan Bryant wrote:
>
>>
>> On Jun 26, 2007, at 11:18 PM, Quôc Peyrot wrote:
>>
>>> It seems that the precision field doesn't work properly with the  
>>> "s" type in Printf.printf:
>>
>> It does work properly.  It's just not working the way you're  
>> expecting it to work.
>
> I was just expecting it to work like the printf from the glibc:
>
> s      If  no  l  modifier  is  present:  The  const char *  
> argument is
> 	      expected to be a pointer to an array of character type   
> (pointer
> 	      to  a string).  Characters from the array are written up to  
> (but
> 	      not including) a terminating NUL character; if  a   
> precision  is
> 	      specified,  no more than the number specified are written.   
> If a
> 	      precision is given, no null character need be  present;  if   
> the
> 	      precision  is  not specified, or is greater than the size of  
> the
> 	      array, the array must contain a terminating NUL character.

The OCaml standard library isn't glibc.  The implementation of the  
Printf/Scanf modules is custom, OCaml specific and tied into the  
compiler, so one should not assume the behave the same way.  They are  
not simply wrappers.  As a matter of fact, they have several other  
differences from the glibc printf family of functions (look at the  
conversion specifiers in the docs).

>
>>> # Printf.printf "%.2s" "qwerty";;
>>> qwerty- : unit = ()
>>>
>>> This should print "qw"
>>
>> No it shouldn't.  The width/precision specifier guarantees a  
>> _minimum_ length for strings, not an absolute length.  From the  
>> docs for Printf:
>
> As said above, this is not how printf is working in the glibc (at  
> least on linux and Mac OS X). Any clue why the same convention has  
> not been followed?

See above.

>
> -- 
> Best Regards,
> Quôc
>
>
>
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