Enum to string in C++11

Question

I realize this has been asked before more than once on SO but I couldn\'t find a question explicitly looking for a current solution to this issue with C++11, so here we go again

Answer 1

As mentioned, there is no standard way to do this. But with a little preprocessor magic (similar to AlejoHausner's second contribution) and some template magic, it can be fairly elegant.

Include this code once:

#include 
#include 

#define ENUM_VALS( name ) name,
#define ENUM_STRINGS( name ) # name,

/** Template function to return the enum value for a given string
*  Note: assumes enums are all upper or all lowercase,
*        that they are contiguous/default-ordered,
*        and that the first value is the default
*  @tparam ENUM     type of the enum to retrieve
*  @tparam ENUMSIZE number of elements in the enum (implicit; need not be passed in)
*  @param valStr   string version of enum value to convert; may be any capitalization (capitalization may be modified)
*  @param enumStrs array of strings corresponding to enum values, assumed to all be in lower/upper case depending upon
*  enumsUpper
*  @param enumsUpper true if the enum values are in all uppercase, false if in all lowercase (mixed case not supported)
*  @return enum value corresponding to valStr, or the first enum value if not found
*/
template 
static inline ENUM fromString(std::string &valStr, const char *(&enumStrs)[ENUMSIZE], bool enumsUpper = true) {
    ENUM e = static_cast< ENUM >(0); // by default, first value
    // convert valStr to lower/upper-case
    std::transform(valStr.begin(), valStr.end(), valStr.begin(), enumsUpper ? ::toupper : ::tolower);
    for (size_t i = 0; i< ENUMSIZE; i++) {
        if (valStr == std::string(enumStrs[i])) {
            e = static_cast< ENUM >(i);
            break;
        }
    }
    return e;
}

Then define each enum like so:

//! Define ColorType enum with array for converting to/from strings
#define ColorTypes(ENUM) \
    ENUM(BLACK) \
    ENUM(RED) \
    ENUM(GREEN) \
    ENUM(BLUE)
enum ColorType {
    ColorTypes(ENUM_VALS)
};
static const char* colorTypeNames[] = {
    ColorTypes(ENUM_STRINGS)
};

You only have to enumerate the enum values once and the code to define it is fairly compact and intuitive.

Values will necessarily be numbered in the default way (ie, 0,1,2,...). The code of fromString() assumes that enum values are in either all uppercase or all lowercase (for converting from strings) that the default value is first, but you can of course change how these things are handled.

Here is how you get the string value:

ColorType c = ColorType::BLUE;   
std::cout << colorTypeNames[c]; // BLUE

Here is how you set the enum from a string value:

ColorType c2 = fromString("Green", colorTypeNames); // == ColorType::GREEN