RE: [boost] Re: static sized strings

From: Martin Bosticky (mbosticky_at_[hidden])
Date: 2004-05-13 03:10:25

I have already written code that allows me to create std like strings of
fixed upper bound length.

If such thing doesn't exist in boost, I am willing to submit and help
standardise my code.

Eg.

// create a string with upper bound length of 4 characters.

boost::slstring<4> myLimitedString;

My implementation has the ability to quickly copy between strings with
the same upper bound (ie without checking the max length). But during
assignments from char* or normal std::string objects or strings with
different upper bound, the upper bound condition is checked and
exception is thrown if there is an error.

Martin.

Martin Bosticky
Software Engineer
Action Information Management Ltd.
Tel: [phone]
Fax: [phone]
Email: mbosticky_at_[hidden]

-----Original Message-----
From: John Nagle [mailto:nagle_at_[hidden]] 
Sent: 12 May 2004 23:00
To: boost_at_[hidden]
Subject: [boost] Re: static sized strings

Reece Dunn wrote:
> Rob Stewart wrote:
> 
>> From: John Nagle <nagle_at_[hidden]>
>> >
>> >    STL strings are variable-sized, with no limit.  When you
>> > add characters, "size()" increases.  Should fixed-size
>>                                                     ^^^^
>> I presume you're referring to fixed-capacity strings which can
>> have a variable size, right?

   Yes.

> yup. The idea is to make it a buffer-overflow safe replacement for C 
> style character buffers, e.g.:
> 
>   char buf[ 100 ];
>   ::sprintf( buf, "...", ... );

   Yes.

>> If the string if (sic) fixed-capacity *and* there remains sufficient
>> capacity, c_str() can null terminate the buffer.  If there isn't
>> sufficient remaining capacity, then throw an exception.

  Done that way, if you write

        char_string<4> s;
        strcat(s,"ABCDE");		// truncates at "ABCD", no null.
        printf("s=%s\n",s.c_str());	// c_str throws exception

which is quite different from classic <string.h> semantics.
You couldn't use that as a drop-in replacement for C strings.
Nor is it compatible with STL basic_string semantics.
I'd suggest consistent null-terminated semantics for char_string.

>> IOW, make it a runtime error to fix the capacity too small to
>> permit null termination when calling c_str().  That still leaves
>> room for things like the 4-character file signature to which you
>> referred, and yet prevents buffer overrun, but doesn't require
>> foregoing flexibility.

   If you want a 4-char file signature, you can use
"boost::array<char,4>", which does that job.  Is there any
real need for that functionality in char_string?
char_string might have some convenience template functions to
interconvert "boost::array" and "boost::char_string".
 
> That is a good idea. It will mean keeping track of the string length, 
  
   Yes, that seems to be necessary.

What about the base class issue?  There's a need to be able to
write something like "char_string_base& s" when you want to
pass around fixed-capacity strings of more than one capacity.

> Regards,
> Reece

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