Re: Could you make this snippet more efficient
pedagani@gmail.com wrote:
On Dec 3, 11:50 am, "Victor Bazarov" <v.Abaza...@comAcast.net> wrote:
pedag...@gmail.com wrote:
On Dec 3, 11:37 am, "Victor Bazarov" <v.Abaza...@comAcast.net>
wrote:
pedag...@gmail.com wrote:
Dear comp.lang.c++,
Could you make this snippet more efficient? As you see I have too
many variables introduced in the code.
//Read set of integers from a file on line by line basis in a STL
set //fp is pre-defined
for(;!fp.eof();)
{
string linestr;
getline(fp,linestr);
istringstream strstreamline(linestr);
istream_iterator<unsigned int> intstream(strstreamline);
set<unsigned int> pckset;
What's that for?
copy ( intstream , istream_iterator<unsigned int>() ,
inserter(modpckset,modpckset.begin ( ) ));
}
V
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*Correction* 'pckset' should have been 'modpckset'.
OK. The entire snippet can be made more efficient by removing
the lines between
getline(fp, linestr);
and
}
; they do essentially no work that would have side effects.
The creation of a stringstream, reading stuff from it, and
putting those unsigned ints into a local set are a waste of
CPU cycles.
V
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Insightful perspective. It just me that I dont have to necessarily
deal them as integers and could consider them as strings instead.
Appreciate your help.
However, I need to store the parsed result in a container on which I
could apply set_difference algorithm. Looks like I must resort to
stringstream in this case. Please correct me if I am wrong.
If you have to convert them, you should use some kind of conversion
function, be it strtod, sscanf, or istream::operator>>. Actually,
it is quite possible that operator>> internally uses strtod.
If storing them in a set is a requirements, you probably need to
do your 'copy' with the second argument being 'inserter' for some
other, non-local set.
It is possible that once the string is read, you might have better
luck using 'strtod' yourself (essentially replacing what operator>>
does, skipping WS, etc.) However, without measuring it's hard to
say what area of your algorithm you need to address.
V
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