Easy way to use variables of enum types as string in C?

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太阳男子 2020-11-22 08:47

Here\'s what I am trying to do:

typedef enum { ONE, TWO, THREE } Numbers;

I am trying to write a function that would do a switch case sim

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执念已碎 (楼主)

2020-11-22 09:15

I have created a simple templated class streamable_enum that uses stream operators << and >> and is based on the std::map:

#ifndef STREAMABLE_ENUM_HPP
#define STREAMABLE_ENUM_HPP

#include 
#include 
#include 

template 
class streamable_enum
{
public:
    typedef typename std::map tostr_map_t;
    typedef typename std::map fromstr_map_t;

    streamable_enum()
    {}

    streamable_enum(E val) :
        Val_(val)
    {}

    operator E() {
        return Val_;
    }

    bool operator==(const streamable_enum& e) {
        return this->Val_ == e.Val_;
    }

    bool operator==(const E& e) {
        return this->Val_ == e;
    }

    static const tostr_map_t& to_string_map() {
        static tostr_map_t to_str_(get_enum_strings());
        return to_str_;
    }

    static const fromstr_map_t& from_string_map() {
        static fromstr_map_t from_str_(reverse_map(to_string_map()));
        return from_str_;
    }
private:
    E Val_;

    static fromstr_map_t reverse_map(const tostr_map_t& eToS) {
        fromstr_map_t sToE;
        for (auto pr : eToS) {
            sToE.emplace(pr.second, pr.first);
        }
        return sToE;
    }
};

template 
streamable_enum stream_enum(E e) {
    return streamable_enum(e);
}

template 
typename streamable_enum::tostr_map_t get_enum_strings() {
    // \todo throw an appropriate exception or display compile error/warning
    return {};
}

template 
std::ostream& operator<<(std::ostream& os, streamable_enum e) {
    auto& mp = streamable_enum::to_string_map();
    auto res = mp.find(e);
    if (res != mp.end()) {
        os << res->second;
    } else {
        os.setstate(std::ios_base::failbit);
    }
    return os;
}

template 
std::istream& operator>>(std::istream& is, streamable_enum& e) {
    std::string str;
    is >> str;
    if (str.empty()) {
        is.setstate(std::ios_base::failbit);
    }
    auto& mp = streamable_enum::from_string_map();
    auto res = mp.find(str);
    if (res != mp.end()) {
        e = res->second;
    } else {
        is.setstate(std::ios_base::failbit);
    }
    return is;
}

#endif

Usage:

#include "streamable_enum.hpp"

using std::cout;
using std::cin;
using std::endl;

enum Animal {
    CAT,
    DOG,
    TIGER,
    RABBIT
};

template <>
streamable_enum::tostr_map_t get_enum_strings() {
    return {
        { CAT, "Cat"},
        { DOG, "Dog" },
        { TIGER, "Tiger" },
        { RABBIT, "Rabbit" }
    };
}

int main(int argc, char* argv []) {
    cout << "What animal do you want to buy? Our offering:" << endl;
    for (auto pr : streamable_enum::to_string_map()) {          // Use from_string_map() and pr.first instead
        cout << " " << pr.second << endl;                               // to have them sorted in alphabetical order
    }
    streamable_enum anim;
    cin >> anim;
    if (!cin) {
        cout << "We don't have such animal here." << endl;
    } else if (anim == Animal::TIGER) {
        cout << stream_enum(Animal::TIGER) << " was a joke..." << endl;
    } else {
        cout << "Here you are!" << endl;
    }

    return 0;
}

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