[boost] Re: static sized strings

From: John Nagle (nagle_at_[hidden])
Date: 2004-05-12 16:59:52

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