[boost] Re: static sized strings

From: John Nagle (nagle_at_[hidden])
Date: 2004-05-10 13:13:46

   There are fundamental issues with string size that have to be
resolved.

   STL strings are variable-sized, with no limit.  When you
add characters, "size()" increases.  Should fixed-size
strings be similar?  If the STL string operations are
to be meaningful, they have to be.  

   In STL strings, "size" doesn't include a trailing null.
Using "c_str" can result in expanding the string to add a
trailing null.  With fixed-size strings, we don't have that
option.

   If c_str is provided, there must always be space
for a trailing null.  So you can't use char_string
when you need a specific fixed length, as for Macintosh
4-character file signatures.  Perhaps "boost::array<char>"
is the way to go for that sort of thing.  Trying to do
both null-terminated and non-null-terminated strings
in the same class will get ugly.  

   Top priority, I think, is a size policy.

   Is Dunn's version in the Boost sandbox?  Where?

                                John Nagle
                                Animats

Reece Dunn wrote:
> John Nagle wrote:
> 
>> John Nagle wrote:
>>
>>>    I've been doing some work on this too.  I made char_string
>>> a subclass of a non-templated char_string_base, so you can
>>> pass references to char_string_base.  This has the disadvantage
>>> of requiring a vtable, but makes the class much more useful.
>>>
>>>    I'll put this someplace publicly visible in the next day
>>> or two.
>>
>>
>>  It's at
>>     http://www.animats.com/source
>> Take a look and see if you like the direction this is going.
>> Thanks.
> 
> 
> Hmm. Which way to go? My latest version has been generalized to 
> incorporate char/wchar_t support, so you can use wide-character strings. 
> It also uses a StringPolicy class (i.e. char_traits) so you can control 
> the length, copy, comparison, etc functions that are used.
> 
> BTW: the reason I use the const char( & s )[ m ] on compilers that 
> support it is because this picks up the string literals in order to 
> remove a call to strlen, thus improving performance.
> 
> Which design do you like better: using a virtual base class, or using a 
> policy template? I have been working on providing an interface similar 
> to std::basic_string, hence some of my latest design choices.
> 
> Ideally, the class should:
> *  safeguard against buffer overflow on static-sized character arrays;
> *  interoperate with classic C string operations;
> *  interoperate with std::basic_string;
> *  provide support for null-terminated strings and also fixed-length 
> strings;
> *  prevent silly mistakes by the user, ideally providing compile-time 
> errors wherever possible.
> 
> At the moment, both implementations provide a different subset of those 
> aims. Do you mind if I look into this and let you know what I come up with.
> 
> Regards,
> Reece