String to enum in C++

Question

Is there a way to associate a string from a text file with an enum value?

The problem is: I have a few enum values stored as string in a text file which I read on the fly on meeting some condition... Now I want to assign the read value to an enum.

What is the most effective way to do so? It doesn't need to be the simplest approach.

Solution 1

You can set up a map that you can use over and over:

template <typename T>
class EnumParser
{
    map <string, T> enumMap;
public:
    EnumParser(){};

    T ParseSomeEnum(const string &value)
    { 
        map <string, T>::const_iterator iValue = enumMap.find(value);
        if (iValue  == enumMap.end())
            throw runtime_error("");
        return iValue->second;
    }
};

enum SomeEnum
{
    Value1,
    Value2
};
EnumParser<SomeEnum>::EnumParser()
{
    enumMap["Value1"] = Value1;
    enumMap["Value2"] = Value2;
}

enum OtherEnum
{
    Value3, 
    Value4
};
EnumParser<OtherEnum>::EnumParser()
{
    enumMap["Value3"] = Value3;
    enumMap["Value4"] = Value4;
}

int main()
{
    EnumParser<SomeEnum> parser;
    cout << parser.ParseSomeEnum("Value2");
}

Solution 2

std::map< string, enumType> enumResolver;

Solution 3

I agree with many of the answers that std::map is the easiest solution.

If you need something faster, you can use a hash map. Perhaps your compiler already offers one, such as hash_map or the upcoming standard unordered_map, or you can get one from boost. When all the strings are known ahead of time, perfect hashing can be used as well.

Solution 4

Accepted answer doesn't contain full listing. I'm adding EnumParser.h which I created from the accepted answer, hope it can help

#include <string>
#include <map>

using namespace std;

template <typename T> class EnumParser
{
    map<string, T> enumMap;
public:
    EnumParser(){};

    T ParseSomeEnum(const string &value)
    { 
        typename map <string, T>::const_iterator iValue = enumMap.find(value);
        if (iValue  == enumMap.end())
            throw runtime_error("");
        return iValue->second;
    }
};

Usage is simple:

enum FieldType
{
    Char,
    Integer,
    Long,
    Fixed,
    Price,
    Date,
    Time
};

EnumParser<FieldType>::EnumParser()
{
    enumMap["Char"] = Char;
    enumMap["Integer"] = Integer;
    enumMap["Long"] = Long;
    enumMap["Fixed"] = Fixed;
    enumMap["Price"] = Price;
    enumMap["Date"] = Date;
    enumMap["Time"] = Time;
}

use:

 EnumParser<FieldType> fieldTypeParser;
 FieldType val = fieldTypeParser.ParseSomeEnum(stringValue)

Solution 5

Look at Boost.Bimap, it provides bidirectional associations between two sets of values. You can also choose the underlying container.

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