Re: Special Data Type Declaration and Usage
On Nov 16, 5:16 pm, Jorgen Grahn <grahn+n...@snipabacken.se> wrote:
On Wed, 2011-11-16, Nick Keighley wrote:
On Nov 15, 9:30 pm, mrc2...@cox.net (Mike Copeland) wrote:
In article <op.v40apype4vp...@gp.homenet.telecomitalia.it>,
gennaro.prota+Use...@gmail.com says...> On Tue, 15 Nov 2011 22:04:25 +=
0100, Mike Copeland <mrc2...@cox.net> wrote:
I need to declare an enormous array (100,000 members) of a =
small
scalar object, and I want to populate it with default values and c=
hange
some of them as needed throughout the processing. The range of =
distinct
values for each element is 0-15, so I could use a 4 bit "mini-byte=
"
the common term for a 4-bit quantity is a "nibble"
...
there are bit fields but I've never been keen. I normally use explicit
masks and shifts to extract bit fields. Something like this:-
<code>
typedef unsigned char Byte;
typedef unsigned char Nibble;
class NibbleContainer
{
public:
NibbleContainer(size_t size, Nibble default_value = 0);
size_t size() const { return m_size; }
void set (size_t i, Nibble nib);
Nibble get (size_t i) const;
private:
size_t m_size;
std::vector<Byte> m_vec;
};
...
</code>
now that amount of c-like c++ is bound to provoke a reaction...
If all C-like C++ was /that/ C++-like, I wouldn't dislike it so much!
Seriously, it looked perfectly fine. I'd do it exactly like that
(except I probably would use 'unsigned' instead of that 'Nibble'
typedef).
I was trying to express the semantics that it was intended to hold
only 4 bits rather than 8. But without the cost of full-blown class.
Even if my class doesn't serve his purpose once he's encapsulated it
he can change the representation without it messing up the rest of his
program. It can be a straight vector (as other posters have suggested)
or my packed representation or a sparse array (or hash or tree). etc.
etc.
A good software engineerign lesson is if you have hard decision (or
any decsion!) to make then hide it from the rest of the program. In C+
+ a class is often a good way to do this (not to denigrate templates
etc.).