How to Efficiently Convert Enum Variables to Strings in C and C ?

How to Convert Enum Variables to Strings in C and C

Converting enum values to strings can be a challenge, especially when we desire a concise solution. This article explores two methods for achieving this conversion: manual string conversion and automated string conversion using the Boost.Preprocessor library.

Manual String Conversion

The simplest approach is to create a function for each enum type that maps values to corresponding strings. For example:

enum OS_type { Linux, Apple, Windows };

const char* os_type_to_str(OS_type os) {
    switch (os) {
        case Linux:   return "Linux";
        case Apple:   return "Apple";
        case Windows: return "Windows";
        default:      return "Unknown OS_type";
    }
}

However, this method becomes tedious when managing multiple enum types.

Automated String Conversion with Boost.Preprocessor

Boost.Preprocessor offers a more elegant and efficient solution. It allows us to generate string conversion functions at compile time based on provided enum names.

#include <boost/preprocessor.hpp>

#define X_DEFINE_ENUM_WITH_STRING_CONVERSIONS_TOSTRING_CASE(r, data, elem)    \
    case elem : return BOOST_PP_STRINGIZE(elem);

#define DEFINE_ENUM_WITH_STRING_CONVERSIONS(name, enumerators)                \
    enum name {                                                               \
        BOOST_PP_SEQ_ENUM(enumerators)                                        \
    };                                                                        \
                                                                              \
    inline const char* ToString(name v)                                       \
    {                                                                         \
        switch (v)                                                            \
        {                                                                     \
            BOOST_PP_SEQ_FOR_EACH(                                            \
                X_DEFINE_ENUM_WITH_STRING_CONVERSIONS_TOSTRING_CASE,          \
                name,                                                         \
                enumerators                                                   \
            )                                                                 \
            default: return "[Unknown " BOOST_PP_STRINGIZE(name) "]";         \
        }                                                                     \
    }

Using this macro, we can define our OS_type enum as follows:

DEFINE_ENUM_WITH_STRING_CONVERSIONS(OS_type, (Linux)(Apple)(Windows))

This macro generates both the enum itself and a corresponding ToString function that maps enum values to strings.

Example Usage

To use the generated ToString function, simply call it like so:

OS_type t = Windows;
std::cout << ToString(t) << " " << ToString(Apple) << std::endl;

This will output:

Windows Apple

Conclusion

By leveraging the Boost.Preprocessor library, we can automate the generation of string conversion functions for enum types. This eliminates the need for manual string mappings and ensures consistency across different enum types, making code maintenance more efficient.

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