enum Type { A=1, B, C };

If I request through cin>> number, then how can I list an element of an enumeration using this number? For example I entered 2, I printed B

Searched in Google, did not find ... all examples for C #

  • one
    In С++ this behavior is not provided. You might as well ask: "how to type the name of a variable whose address the pointer stores." - mega
  • but no way, except how to write your function to convert / output. Some people make their own macros for this. - KoVadim
  • Can be done through map - skegg
  • OK, I realized that the simple way is not to do this, only through dancing with a tambourine: / - Comfmore
  • So this is C ++, not a python))) - skegg

3 answers 3

Good day! The answer to your question depends on what you want to receive. If you want to get the name of an enumeration item, then you need to overload the input / output statements to the stream. I learned this technique from the book by B. Straustrup "Design and Evolution of C ++" (I strongly advise you to read it - you can learn a lot from this). If you just want to know the element of the enumeration itself, then use static_cast to safely cast.

 #include <iostream> #include <string> #include <stdexcept> enum Type { A = 0, B, C }; std::ostream& operator << (std::ostream& out, const Type& t) { switch(t) { case A: return (out << "A"); case B: return (out << "B"); case C: return (out << "C"); } return (out); } std::istream& operator >> (std::istream& input, Type& t) { std::string s; input >> s; if (s == "A") { // неявная конвертация в Type t = A; } else if (s == "B") { t = B; } else if (s == "C") { t = C; } else { // здесь можно выкинуть исключение throw std::runtime_error("incorrect input"); } return (input); } int main(int argc, char *argv[]) { using namespace std; Type type; try { cin >> type; } catch(std::exception& e) { cout << e.what(); return 1; } cout << type << "=" << static_cast<int>(type); return 0; }

The variant with an associative array also has a right to exist, but one has to pay with memory overruns, and additionally, transfers usually rarely change, so it will not be difficult to insert a couple of lines later.

    Well, for example, it was possible to google for the query "c ++ enum to string" and good Google would give you the very first result of this. Some simple witchcraft on your part, and everything works

    • Awesome answer. Referring to SO, where it is still not obvious that they are responding correctly. - avp pm
    • Well, why, the norms of the answer ... everything is so many there + I noticed a link to a similar topic there, where there is also a great discussion. I just wrote various versions in Russian in Google, so I didn’t get there. - Comfmore
    • @Comfmore, in SO only one answer (with map) is correct. In the others it is implicitly assumed that enum variables used as indices have the values ​​0, 1, ... And this language does not guarantee. - avp

    Look for char *, likewise for int

     enum ex {A, B, C, NONE}; struct enex { ex en; const char *name; }; static ex get_enum (const char *name) { static struct enex en[] = {{A,"A"},{B,"B"},{C,"C"},{A,0}}; for (int i = 0; en[i].name; i++) if (strcmp(name,en[i].name) == 0) return en[i].en; return NONE; }
    • one
      well, too tricky, then it can be easier in the get_enum function to make a switch and return a string by digit: case 1: return "A"; etc. - Comfmore
    • This is essentially meaningless. After all, it simply creates an array of enumerations. It's easier to use an ordinary array. If there is such a need for "numbering" ENUM, then you can, for example, use the associative container Map <T> from STL or create a static array. Well, or if there are not so many elements, then you can set them all in constants. - AseN
    • Perhaps (seeing cin >> ) I misunderstood the question. I decided that it was required to return enum by the entered numerical value, but wrote a return for the entered name . In general, the comparison between enum and int compiler (g ++) permits, so for numeric values ​​you can simply search the integer in the array of enums and return the enum. But, it is somehow ugly ("dumb"). - avp