I have a bunch of enum types in some library header files that I'm using, and I want to have a way of converting enum values to user strings - and vice-versa.
RTTI won't do it for me, because the 'user strings' need to be a bit more readable than the enumerations.
A brute force solution would be a bunch of functions like this, but I feel that's a bit too C-like.
enum MyEnum {VAL1, VAL2,VAL3};
String getStringFromEnum(MyEnum e)
{
switch e
{
case VAL1: return "Value 1";
case VAL2: return "Value 2";
case VAL1: return "Value 3";
default: throw Exception("Bad MyEnum");
}
}
I have a gut feeling that there's an elegant solution using templates, but I can't quite get my head round it yet.
UPDATE: Thanks for suggestions - I should have made clear that the enums are defined in a third-party library header, so I don't want to have to change the definition of them.
My gut feeling now is to avoid templates and do something like this:
char * MyGetValue(int v, char *tmp); // implementation is trivial
#define ENUM_MAP(type, strings) char * getStringValue(const type &T) \
{ \
return MyGetValue((int)T, strings); \
}
; enum eee {AA,BB,CC}; - exists in library header file
; enum fff {DD,GG,HH};
ENUM_MAP(eee,"AA|BB|CC")
ENUM_MAP(fff,"DD|GG|HH")
// To use...
eee e;
fff f;
std::cout<< getStringValue(e);
std::cout<< getStringValue(f);
If you want the enum names themselves as strings, see this post.
Otherwise, a std::map<MyEnum, char const*>
will work nicely. (No point in copying your string literals to std::strings in the map)
For extra syntactic sugar, here's how to write a map_init class. The goal is to allow
std::map<MyEnum, const char*> MyMap;
map_init(MyMap)
(eValue1, "A")
(eValue2, "B")
(eValue3, "C")
;
The function template <typename T> map_init(T&)
returns a map_init_helper<T>
.
map_init_helper<T>
stores a T&, and defines the trivial map_init_helper& operator()(typename T::key_type const&, typename T::value_type const&)
. (Returning *this
from operator()
allows the chaining of operator()
, like operator<<
on std::ostream
s)
template<typename T> struct map_init_helper
{
T& data;
map_init_helper(T& d) : data(d) {}
map_init_helper& operator() (typename T::key_type const& key, typename T::mapped_type const& value)
{
data[key] = value;
return *this;
}
};
template<typename T> map_init_helper<T> map_init(T& item)
{
return map_init_helper<T>(item);
}
Since the function and helper class are templated, you can use them for any map, or map-like structure. I.e. it can also add entries to std::unordered_map
If you don't like writing these helpers, boost::assign offers the same functionality out of the box.