Cannot make unordered_map work - c++

Question

I have written fairly simple code to check out unordered_pair
// unordered_map example
#include <iostream>
#include <unordered_map>
int main (){
std::unordered_map<double, double> mymap = {
{5,2.3},
{7,34},
{4,12}
};
std::cout<<":::: unordered_map ::::"<<std::endl;
std::cout<<"5 ->"<<mymap[5]<<std::endl;
std::cout<<"7 ->"<<mymap[7]<<std::endl;
std::cout<<"4 ->"<<mymap[4]<<std::endl;
std::cout<<"Done ! ";
return 0;
}
I get the following error
unordered_map.cpp:5:37: error: non-aggregate type 'std::unordered_map<double, double>' cannot be initialized with an initializer list
std::unordered_map<double, double> mymap = {
^ ~
1 error generated.
Compilation failed
I am working on OSX and using geany.
Build command in Geany is :
g++ -Wall -c "%f"

Answer 1

unordered_map was introduced in the C++11 standard. If your g++ version supports it, you can enable c++11 standard with option -std=c++11
is there a way to use associative containers in older standards
std::map is an associative container. It exists in all c++ standards.
I was trying to use unordered_map because it is faster than map
unordered_map is faster in some cases. map is faster in other cases. Don't assume one way until you have measured.
However, using map without -std=c++11 still gives me same error as above
That's because you use list initialization which also requires c++11.
The old way of initializing a map:
std::map<int, int> m;
m[1] = 3;
m[2] = 2;
m[3] = 1;
Boost has a neat template for similar syntax to list initialization:
map<int,int> next = map_list_of(1,2)(2,3)(3,4)(4,5)(5,6);