Re: what is more effective: std::strings or numbers?
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