Re: STL stable_sort sorting issue

From:
"Daniel T." <daniel_t@earthlink.net>
Newsgroups:
comp.lang.c++,comp.lang.c++.moderated
Date:
Tue, 29 May 2007 16:13:34 CST
Message-ID:
<daniel_t-4490F8.15415229052007@news.west.earthlink.net>
In article <1180442852.291017.240950@k79g2000hse.googlegroups.com>,
 sandy <sandip.ware@gmail.com> wrote:

Hello C++ Guru,
  I am using STL stable_sort to sort the vector string data using
below code.

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;

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;
}

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

When I am expecting result like below :.

AAA
aaa
BBB
bbb

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


Because they are put in your container first. "stable_sort" tries to
maintain the existing order of the items as best it can. Since your code
says that "aaa" and "AAA" are equal, it doesn't swap them.

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