can I rely on the sorting of std::map<>

[jabbah]

I have some data in a map and I want to sort it. Currently I have implemented it like this:

#include <iostream>
#include <map>
#include <string>
using namespace std;
 
int main(){
 
  // some data
  map<string, double> myList;
  myList["peter"]= 3.0;
  myList["paul"]= 1.0;
  myList["mary"] = 2.0;
 
  // sort the elements
  map<double, string> mySortedList;
  for ( map<string, double>::iterator i = myList.begin();
    i != myList.end();
    i++ )
    {
      mySortedList[ i->second ] = i->first;
    }
 
  // print the sorted elements
  cout << "sorted: ";
  for ( map<double, string>::iterator i = mySortedList.begin();
    i != mySortedList.end();
    i++ )
    {
      cout << i->first << " {" << i->second << "} ";
    }
  cout << "\n";
 
}
 

And it works as I expect it with g++ 3.4.4 cygwin, but I'm anxious since
http://www.cppreferenc e.com/cppmap/index.html
only says that maps are sorted, but not whether that is ascending or descending or whatever-map-blackmagic-sorting.

Anybody able to clarify this?

[weaknessforcats]

maps are sorted.

They are sorted by the operator< of the class used as the key.

If there is no operator< for the class used as a key, you can write an operator< that takes two key valus as argument and returns a bool.

OR, you can write any function that takes two key objects, compares them and returns a bool.

The sequence you get is determined by the comparision function and not by the map.

The map template has:

map<key, value, func>

where key is the key object, valus is the object associated with the key, and func is a binary predicate. In STLspeak, a binary predicate is a function thay takes two arguments and returns a bool. For example, yo use any old compare function, you could:

map<int, string, Ascending> myMap;
 
bool Ascending(int first, int second)
{
    return first < second;
}
 
OR:
 
map<int, string, Descending> myMap;
 
bool Descending(int first, int second)
{
    return first > second;
}
 

[jabbah]

ok, got it, thank you