C++ enum [string] error

Question

I am using an enum to declare types of variables. However, I get an error on each string saying: Error: expression must be an integral constant expression. And if I change the "" to '', the words which are five characters or over give the error: Error: too many characters in a character constant. What should I do?

typedef enum
{
    INT = "int",
    STRING = "string",
    BOOLEAN = "bool",
    CHARACTER = "char",
    DOUBLE = "double",
    FLOAT = "float",
    LONG = "long",
    SHORT = "short"
} variable_types;

Use integral constant expressions, as the compiler error suggests. — juanchopanza, Nov 29 '13 at 15:48
Check [here](http://stackoverflow.com/questions/12557164/declaring-the-underlying-type-of-enumeration-identifier) — , Nov 29 '13 at 15:49
Can we use a class with `static const std::string`s as a substitute for the enum? I was starting to answer this, but I could find no reference to someone using this. — Jupotter, Nov 29 '13 at 16:02

score 2 · Answer 1 · edited May 23 '17 at 12:19

2

I don't think enums can be mapped to characters / strings. You can use an std::map<> to map the values to string values.

How to easily map c++ enums to strings

edited May 23 '17 at 12:19

Community

1
1

answered Nov 29 '13 at 15:49

ApplePie

8,814
5
39
60

Note that you can just use a vector instead of a map (as suggested in the link), if you don't need the enums to have special numeric values. – Domi Nov 29 '13 at 15:52

Paweł Stawarz · Accepted Answer · 2013-11-29T15:55:52.590

The enum type wasn't made for representing strings. IF you read a bit about it, you'll notice it stores only int types inside. If you need to map values like that, enum isn't really a good choice.

If you want to keep your syntax, use the #define command:

#define INT "int"
#define STRING "string"
...
#define SHORT "short"

You can also combine your current code with a std::map:

#include <map>
typedef enum
{
    INT,
    STRING,
    ...
    SHORT
} enumeratedTypes;
map<enumeratedTypes,string> variable_types;
variable_types[INT] = "int";
variable_types[STRING] = "string";
...
variable_types[SHORT] = "short";

Or just check things via an switch statement, if you need it for a function:

string foo(enumeratedTypes type){
   int choice = type;
   switch(choice){
   case INT:
      return "int";
   case STRING:
      return "string";
   ...
   case SHORT:
      return "short";
   default:
      return "error";
 }

score 1 · Answer 3 · answered Nov 29 '13 at 15:49

Enums must be integral values. If you want, you can then use the enum values as indices into an array of strings.

Like so:

#include <vector>
#include <string>

enum variable_types
{
    INT,
    STRING,
    BOOLEAN,
    CHARACTER,
    DOUBLE,
    FLOAT,
    LONG,
    SHORT
};

// ...

const std::vector<std::string> enumNames = { "int", "string", "bool", ... };
variable_types someEnum = ...;
auto enumName = enumNames[someEnum];

score 1 · Answer 4 · answered Nov 29 '13 at 15:50

1

As far as I know C/CPP standard does not support string-value enumerations. The value of the enumerations must be an integer (signed-unsigned and length depends on compiler)

If you put your string in '' marks that means that the string shall be interpreted as a character and - of course - a character has an integer value (0-255). Since in the marks there are more than one character the compiler will complain.

answered Nov 29 '13 at 15:50

tebe

316
1
8

A best practice is to map enum values to strings is to create a struct: typedef struct { my_enum_type enumval; std::string enumstring} Then you can define a function to look the string up – tebe Nov 29 '13 at 15:51
Or - if your enum starts with 0 and is strict ascending you can use the enum to address the above mentioned array. But be careful, if you add an enum entry you have to add a struct-array entry as well otherwise you may crash or get an invalid string – tebe Nov 29 '13 at 15:53

C++ enum [string] error

4 Answers4