While adding Serialization support to my project, I realized that I would require some way to convert a
string to an enumerator and vice versa. So I did a Google search for the same, and found a lot of information; different ways in which people implemented this functionality.
However, all the solutions I found suffered from one or more of the following:
- No support for enumerators with non-contiguous values
- No support (not even partial support) for enumerators with duplicate values
- No support for existing enumerations (without modifying their source code)
- Requires one or more extra files per enumeration
- Requires source-code to be pre-processed (by a custom binary) before compilation
- Difficult to use or maintain
- Highly susceptible to typos
- Is platform/compiler specific (not portable)
So (the rip-off that I am), I borrowed the good ideas from all the solutions I found, added a few of my own and mixed-and-matched to create the code which accompanies this article. I don't claim this to be the best solution for every case, just that it solved my problem nicely and that it could be of use to someone else as well.
How To Use the Code
Using the code is quite easy. All we need to do is add one file: EnumString.h (see the source code accompanying this article) to our project.
Let's say we wanted to create an
enum to represent one of the Furious Five Masters (Kung Fu Panda (2008) anyone?). So we go ahead and declare it as usual:
Tigress = 5,
Viper = 3,
Monkey = 4,
Mantis = 1,
Crane = 2
Don't worry about the values assigned, they are simply my rough idea of what the 'mass' of each master is, in some imaginary units. Now to add stringizing support, we need to declare the
enum again, but in a different format (uses helper macros):
Begin_Enum_String( Master )
Enum_String( Tigress );
Enum_String( Viper );
Enum_String( Monkey );
Enum_String( Mantis );
Enum_String( Crane );
And we're done! Note that since this second declaration lies in the same header/source file as the actual
enum definition (probably declared just below it), it's not that difficult to update it whenever we modify the actual enumeration.
Now we can convert from a
string to a
Master enumerator and vice versa, quite easily. The following code shows how to do that:
const std::string &masterStr = EnumString<Master>::From( Monkey );
assert( masterStr.compare( "Monkey" ) == 0 );
Master master = Tigress;
const bool bResult = EnumString<Master>::To( master, masterStr );
assert( bResult == true );
assert( master == Monkey );
Using the Code with Existing Enumerations
Suppose we want to add stringizing support to an existing enumeration from a library, which is namespaced. Imagine that the
enum is declared like this in the library:
Sunday = 1,
Saturday = 7
Say that we can't modify the library files (which is anyway not a good practice). So we create a separate header file in our project, in which we will declare stringizing support for the required library
enum. For the declaration, we have 3 options:
Option 1 - Fully Qualify All the Names
Begin_Enum_String( SomeLibrary::WeekEnd )
Enum_String( SomeLibrary::Sunday );
Enum_String( SomeLibrary::Saturday );
The consequence of this is that the stringized
enums will also be fully qualified names. So, the statement
EnumString<WeekEnd>::From( SomeLibrary::Saturday ) will yield "
SomeLibrary::Saturday", and not just "
Option 2 - Use the 'using namespace' Directive
using namespace SomeLibrary;
Begin_Enum_String( WeekEnd )
Enum_String( Sunday );
Enum_String( Saturday );
Option 3 - Register the Enumerators Yourself
Without using the '
Enum_String' helper macro (see the next section 'How does it actually work?', for an explanation of this):
Begin_Enum_String( SomeLibrary::WeekEnd )
RegisterEnumerator( SomeLibrary::Sunday, "Sunday" );
RegisterEnumerator( SomeLibrary::Saturday, "Saturday" );
How Does It Actually Work?
It's not required to know how it works in order to use it, so those who are not really interested can skip this section. Also, beginners might have to brush up on their C++ before reading this.
If you look at the declarations of the helper macros, you'll see that the definition of the
string support for FuriousFiveMaster, works out to the following:
template <> struct EnumString<Master> :
public EnumStringBase< EnumString<Master>, Master >
static void RegisterEnumerators()
RegisterEnumerator( Tigress, "Tigress" );
RegisterEnumerator( Viper, "Viper" );
RegisterEnumerator( Monkey, "Monkey" );
RegisterEnumerator( Mantis, "Mantis" );
RegisterEnumerator( Crane, "Crane" );
You might have already realized that the above is a specialization of the
EnumString template class. It defines the
RegisterEnumerators function which is used by its base class
EnumStringBase, via CRTP. Now the workings of the usage become clear. When you use the functions
EnumString<Master>::From or EnumString<Master>::To, you're using the version of the
EnumString template class which is specialized with the
As with most things, the code does have some drawbacks. The two most important ones are:
- Doesn't support conversion of enumerators with duplicate values to
strings (although vice versa works just fine). An attempt to convert such an enumerator will yield an empty
string (which can be tested for).
- Conversion performance might be a bottleneck for some applications. A single
std::map is used internally for storing the relationship of enumerators to their
string representations. So lookups during conversions are not in constant time. A conversion from an enumerator to a
string will be in linear time, although a vice versa conversion should be very fast.
Since the code makes extensive use of templates, it may not work with older compilers. The code has been tested with the following compilers:
- Microsoft Visual C++ 2005/2008
- GCC 4.4.0
There is much potential for improvement of the code. But since the current code is good enough for my needs, I'll leave that for someone else to do. If you make changes to the code, improve it, or simply have an entirely different and better way to solve this, please share it with me also; I might just dump my code and use yours instead!
- 3rd September, 2009: Initial post