STL map.find problem in using a compare class

[hagdanan]

Hi all, I am new to STL and I have a problem with my map. I made a class(Sort) for comparison on the map but the problem is map.find will not work.

Can someone explain why find was not able to locate the key?

here is the code:

#include<iostream>
#include<map>
#include<string>
 
using namespace std;
class Sort
{
    public:
        bool operator() (string const &_A, string const &_B) const
        {
            double num1, num2;
            num1 = atoi(_A.c_str());
            num2 = atoi(_B.c_str());
            if( num1 && num2 ) {
                if( num1 <= num2 )
                    return true;
                else return false;
            }
            else {
                if( _A.compare(_B) <= 0 ) return true;
                else return false;
            }
        }
};
 
typedef map<string, string, Sort> EnumMap;
 
int main()
{
  string str="A";
  EnumMap months;
  EnumMap::iterator it;
  months["1"] = "January";
  months["7"] = "July";
  months["2"] = "February";
  months["3"] = "March";
  months["4"] = "April";
  months["5"] = "May";
  months["6"] = "June";
  months["8"] = "August";
  months["9"] = "September";
  months["10"] = "October";
  months["11"] = "November";
  months["12"] = "December";
 
  for ( it=months.begin() ; it!=months.end(); it++ ) {
        cout << (*it).first << "==>" << (*it).second << endl;
  }
 
  EnumMap::iterator t2= months.find("7");
  if(t2!=months.end())
    cout << "Found" << endl;
  else cout << "Not Found" << endl;
}

[newb16]

Comparison operator for map is '<' - strictly less. It checks equality as !(A<B) && !(B<A). So this
# if( num1 <= num2 )
# return true;
should be num1 < num2.

btw, my cygwin compiler doesn't like _B and thinks it's an integer constant.
ctype.h : #define _B 0200

[hype261]

Why are you using std::map<std::string, std::string>? Since all your keys are integers it would be easier to use std::map<int, std::string> and it would be quicker also.

[hagdanan]

@hype261
Because sometimes we use keys that are not in integer form. And map do sort the keys when we insert on it, so if I use keys as "1", "2", "3", "10".. this will not be arrange numerically(since its string) as expected to be 1, 2, 3 and 10.. but this will be arranged alphabetically as "1", "10","2","3". That's why I have this class to check if the string can be converted to integer and compare as integer so I can have the correct sequence.

[hagdanan]

@newb16
Thanks a lot.

but I am wondering about the effect of the Sort class on the find method. I need to return false so that find will work?

[newb16]

You need to return true only if A is less than B. If they are equal return false.