Re: STL stable_sort sorting issue

From:

Alberto Ganesh Barbati <AlbertoBarbati@libero.it>

Newsgroups:

comp.lang.c++.moderated

Date:

Tue, 29 May 2007 17:43:51 CST

Message-ID:

<Az07i.23070$U01.261618@twister1.libero.it>

sandy ha scritto:

bool my_comparison( string p1, string p2)
{
    //Make first string lower case
        string::iterator StringValueIterator = p1.begin();
    transform (p1.begin(),p1.end(), StringValueIterator,toupper);

    //Make second string lower case
       StringValueIterator = p2.begin();
    transform (p2.begin(),p2.end(), StringValueIterator,toupper);

       return p1 < p2;
}

That's the most inefficient way of performing a case-insensitive
comparison...

int main()
{
   typedef vector<string> holder;
   holder some_holder;
   some_holder.push_back("aaa");
   some_holder.push_back("bbb");
   some_holder.push_back("AAA");
   some_holder.push_back("BBB");

   stable_sort(some_holder.begin(),some_holder.end(),my_comparison);
   holder::iterator VectIt = some_holder.begin();
   for( ; VectIt!=some_holder.end(); ++VectIt)
   {
      cout <<*VectIt<< '\n';
   }
   return 0;
}

I got below result :
aaa
AAA
bbb
BBB

That's the correct output.

When I am expecting result like below :.

AAA
aaa
BBB
bbb

Why it's giving preference to first small case why not upper
letter ?

Why do you expect that? The term "stable" in the name stable_sort means
that the order of two strings that are "equivalent" is left unchanged.
As "aaa" and "AAA" are equivalent according to your comparison, then
they must be kept in the original order. The algorithm is not favoring
small case against upper case: try to change the original order and see.

HTH,

Ganesh

--
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]