RE: [boost] static sized strings

From: Reece Dunn (msclrhd_at_[hidden])
Date: 2004-06-03 08:38:53

Martin wrote:
>I have tested the sandbox version of the static sized strings. It works 
>fine
>but there are a few inconveniences that I want to point out.

I have been writing a series of test cases (boost-sandbox/libs/test) and 
fixing several bugs. Have you tried these? Also, what compiler(s) are you 
using?

>1. The abstract base class.
>---------------------------
>Having an ABC to handle fixed strings of various lengths is a good idea but 
>it
>is not very practical. I understand that the main purpose is to allow fixed
>strings to be passed to functions without using templates.
>
>int countwords(const boost::char_string & str);
>
>unfortunatly the ABC makes it difficult to pass anything but fixed strings. 
>If
>you want to pass a string literal, a character array or a std::string you 
>must
>create a temporary fixed_string<>.
>
>countwords(boost::fixed_string<20>("The quick brown fox"));

This is an unfortunate side-affect of using the ABC technique that affects 
John's implementation as well. Your proposed solution looks interesting, but 
I don't know how practical it will be for the string manipulation operations 
(w.r.t. buffer safety).

Rob proposed a "make_string" function, which would simplify this a little.

>2. Substrings
>-------------
>One of the applications I can see for fixed_string is when you want to 
>avoid
>dynamic allocation but still want to use the std::string interface and
>algorithms. In that perspective it seems strange that substr returns a
>std::string instead of a fixed_string.

This is related to the above problem. You cannot create an instance of 
boost::char_string, etc. and as such cannot implement substr in the usual 
way (this is the proplem I was having with operator+). The solution would be 
to defione an alternate substr function in fixed_string, but this would not 
solve the problem for boost::char_string, etc.

The alternative would be to use a ranged string (pointer to the fixed_string 
buffer and length), but the problem with this is null-termination.

I do not see an easy way around this without removing the ABC design, since 
it is not possible to do fixed_string< length() > or something similar.

>3. resize
>---------
>Still missing a method to update the length to reflect the current string
>length. I think a resize without arguments would be a good solution.
>
>boost::fixed_string str<10>
>strtime(str.buffer());
>str.resize();

I'll add this soon. I have mainly been focusing on getting documentation and 
the test cases up.

>4. operator[]
>-------------------------
>I don't have the standard basic_string interface available but I am pretty
>sure that operator[] doesn't throw an exception if the argument is outside
>max_size().

This is a deviation from the standard. If i > capacity() then the index will 
be out of the string buffer range and a buffer overrun can occur. This 
generates an exception to prevent the overrun.

I should add this to the docs.

Regards,
Reece

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