C++ Map with two keys of different values - c++

Question

I need a map which can have two keys, of different data types, yet point to the same struct.
struct DataStruct {
SomeEnum keyEnum; // <---- key as enum
std::string keyString; // <----- a key as a string
int arbitrarydata;
int moredata;
}
Then I want a std::map I can look up like:
std::map<SomeEnum||std::string, DataStruct> dataMap;
dataMap[SomeEnum::AValue] = dataStruct1;
dataMap["mykey"] = dataStruct2;
Is this even possible or do I need to make 2 maps? Seems a waste. Or do I need to overload an operator or something?

Answer 1

You can use std::pair, like this:
#include <iostream>
#include <map>
#include <utility>
typedef enum {A, B, C} en;
int main ()
{
en myen = A;
std::map<std::pair<char,int>, int> mymap;
mymap.insert ( std::pair<std::pair<char, int>,int>(std::make_pair('a',myen),200) );
mymap.insert ( std::pair<std::pair<char, int>,int>(std::make_pair('z',30),400) );
// showing contents:
std::cout << "mymap contains:\n";
for (std::map<std::pair<char,int>, int>::iterator it=mymap.begin(); it!=mymap.end(); ++it)
std::cout << "(" << it->first.first << ", " << it->first.second <<
") => " << it->second << '\n';
return 0;
}
Not an answer in the question:
Note, that in C++11, you can use enum class, which in general can be more useful.

Answer 2

A std::map can only have keys of the same type, but you can trick it with whatever key logic you want. Just be sure that they can compare properly:
struct DataStruct {
struct Key {
std::string keyString;
SomeEnum keyEnum;
int type;
Key(SomeEnum a) : keyEnum(a), type(0) { }
Key(const char * a) : keyString(a), type(1) { }
bool operator<(const Key & o) const {
if (type != o.type) return type < o.type;
else return type == 0 ? keyEnum < o.keyEnum : keyString < o.keyString;
}
};
int data;
}
Then you can use it almost the way you wanted:
std::map<DataStruct::Key, DataStruct> dataMap;
dataMap[SomeEnum::AValue] = dataStruct1;
dataMap["mykey"] = dataStruct2;
You need to be sure that keys of different types don't point to the same data, thats why I first order them by type and then by their value.