Specialize hashmap template

Question

I am using hash_map in C ++ and want to provide a simplified type name for it:

The key type and hash function are always the same.

stdext::hash_map<std::string, [MAPPED TYPE], CStringHasher>

However, I do not want to write all this every time I declare a hash map that displays lines for input X.

• Is it possible to write a template or a macro that simplifies this?

So the above expression would look like this:

template<typename T> StringHashmap = stdext::hash_map<std::string, T, CStringHasher>

StringHashmap<int> mapA; //Maps std::string to int
StringHashamp<bool> mapB; //Maps std::string to bool

Answer 1

As others have said, template aliases are the way to go if you can use C ++ 0x:

template < typename MappedType >
using StringHashMap = stdext::hash_map< std::string, MappedType, CStringHasher >;

StringHashMap< int > mapA;
StringHashMap< bool > mapB;

(As @MSalters noted, if you have C ++ 0x, you should probably use one std::unordered_map.)

Otherwise, you can use the usual workaround, which should define a class template containing typedef:

template < typename MappedType >
struct StringHashMap
{
    typedef stdext::hash_map< std::string, MappedType, CStringHasher > type;
};

StringHashMap< int >::type mapA;
StringHashMap< bool >::type mapB;

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Answer 2

++ (++ 03) . -

#define StringHashMap(type) stdext::hash_map<std::string, type, CStringHasher>

, , :

StringHashMap(pair<int, string>) myMap; // Error!

,

StringHashMap((pair<int), (string>)) myMap; // Error!

, . , . typedef, :

typedef pair<int, int> IntPair;
StringHashMap(IntPair) myMap; // Okay

++ 0x, , , :

template <typename T>
    using StringHashMap = stdext::hash_map<std::string, T, CStringHasher>;

, ++ 03 " typedef", , .

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Answer 3

++ 0x, typedefs , :

http://en.wikipedia.org/wiki/C%2B%2B0x#Template_aliases