Re: what is more effective: std::strings or numbers?
thanks for answering.
i was thinking about enumeration, and the solution looked nice and
effective, but just one thing hurt me: the keywords are not a constant set.
they may be occasionally changed, replaced, added, deleted and so on. i
won't want to recompile the program every time. ;) and i can't stick any
numbers to the keywords, because they can be changed also. all i can lean on
is only the keywords string names.
but maybe you're right - the clearness of the code costs more. and it
doesn't make sense to make the solution more complicated, that it needs to
be. at least searching in map by a string key is pretty fast.
--
alex c.
"Ulrich Eckhardt" <eckhardt@satorlaser.com> wrote in message
news:c7j4k4-7jm.ln1@satorlaser.homedns.org...
Alexander Cherny wrote:
what is more effective: std::strings or numbers?
Yes.
i got a collection of keywords. they are all up to 12 characters, consist
of only lower case english letters, and we may expect, that no new string
will be longer in the collection.
How about just mapping them to an enumeration?
namespace keyword {
enum type {
invalid,
foo,
bar,
num_keywords
};
std::string to_string(type t);
type from_string(string const& str);
}
we can convert such strings to numbers
and identically recover them, say, this way (ms specific):
#include <string>
using namespace std;
const __int64 Str2Num(const string &S)
{
if(S.length() > 12)
return 0;
__int64 n = 0;
for(size_t i = 0; i < S.length(); ++i)
n = n*26+__int64(S[i]-'a'+1);
return n;
}
This is also called 'hashing'. If you know the keywords already, there is
a
tool out there that can generate you a hash function for them, IIRC.
However, you really should consider throwing exceptions instead of
returning default values.
now i want to put my values to an std::map. what will be more effective:
std::map<__int64, something> or std::map<string, something>? __int64
takes
8 bytes, string takes more - 16. but which comparison will be faster -
strings or __int64.
does this converting make sense?
This doesn't make any sense at all. Firstly, you don't need a 64 bit
integer
to represent a handful of keywords. Secondly, you shouldn't try to
micro-optimize your code unless you have measured(!) that the bottleneck
is
exactly there. In that sense, keep your code clean instead and
maintainable
and just map them to an enumeration.
Uli