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From: Phil Endecott (spam_from_boost_dev_at_[hidden])
Date: 2007-05-09 15:40:56

Jens wrote:
> IMHO what this discussion shows is that in this case there's no "obvious" meaning of 8 bit
> integer types (uses seem to be number, character or byte). As far as I am concerned, that
> implies that it's up to the user to supply that meaning, and not for the library to assign
> one.

Yes. But there are two existing ways for the user to say what they mean:

(1) By using int8_t / uint8_t for number-bytes and char for
character-bytes. For this to work we would need to either
   (a) Do some magic so we can distinguish [un]signed char from
[u]int8_t. I believe that's impossible.
   (a) Change the behaviour of standard streams for [un]signed char.
That's not going to happen, and even if it could happen it would
probably break significant amounts of code that uses 'unsigned char'
for characters.
   (b) Change lexical_cast to special case 'unsigned char' and 'signed
char'. This is clearly unpopular with the list though I personally
would be happy with it.
   (c) Allow the user to enable (b) if that is what they want. I get
the impression that this could be done by supplying your own partial
specialisation of lexical_cast; is this true? (Off topic, there is the
question of whether common lexical casts can be made more efficient by
providing specialisations that invoke C library functions like
strtol(); I think someone told me that this wasn't possible, but I
don't think I ever knew why.)

(2) By using format() instead of lexical_cast(). (For to-string
conversions. In principle something symmetric could be provided for
from-string conversions.) Using format, you supply a format specifier
in the style of printf() that indicates whether you want to do a string
or numeric conversion. However, *this format specifier is ignored* and
if you ask for a '%d' int8_t you'll still get a character.

I would much prefer to have one of these existing methods 'do what I
want', rather than invent something else.

I'm going to see if I can write a my_lexical_cast() that uses
lexical_cast by default but changes the behaviour for [un]signed char.


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