c++ enum and using them to input from user

Question

I have an enum in my code that is the following: enum Status {In-Active, Active};. A status object is passed to a Person object as a parameter, so I wa

Answer 1

You can't read enum values directly, you'll need a std::map that maps user input to an enum value.

std::map<std::string,Status> m;
m["In-Active"] = In-Active;
m["Active"] = Active;

std::string sstatus;
cin >> sstatus;
Status status = m[sstatus];

Answer 2

• Enum objects are being parsed at compile time and it can only contain constant integer values.

• Person p(name, age, status); //Here without using status object you should send a value directly like "In-Active" or "Active". So there would be no input from the user regarding th status field.

enum Status {InActive, Active};

• Here Status is a enum class and any object created would contain values "Inactive" or "Active". If you try to assign some other value you would get an compiler error.

Status status;

• Here status is an enum object created and it contains garbage value.

cout << "Enter status: "; cin >> status;

• Here you are asking user for an input for an enum object which is totally invalid for the compiler.

Answer 3

You can also wrap the enum inside a class and provide operator>>. This is a modified example from this link http://en.wikibooks.org/wiki/More_C%2B%2B_Idioms/Type_Safe_Enum

#include <iostream>

template<typename def>
class safe_enum : public def
{
public:
  int val;
  safe_enum(int v) : val(v) {}
//  inner underlying() const { return val; }
  bool operator == (const safe_enum & s) const { return this->val == s.val; }
  bool operator != (const safe_enum & s) const { return this->val != s.val; }
  bool operator <  (const safe_enum & s) const { return this->val <  s.val; }
  bool operator <= (const safe_enum & s) const { return this->val <= s.val; }
  bool operator >  (const safe_enum & s) const { return this->val >  s.val; }
  bool operator >= (const safe_enum & s) const { return this->val >= s.val; }
};

struct status_def {
  enum type { NoValue, InActive, Active };
};
typedef safe_enum<status_def> Status;

std::istream& operator>>(std::istream& Istr, Status& other)
{
    std::cout << "Enter Status value: " << std::endl; 
    //here the logic to handle input error
    Istr >> other.val;
    return Istr;
}

std::ostream& operator<<(std::ostream& os,const Status& toPrint)
{
    if (toPrint.val == Status::Active)
        return os << "Active";
    if (toPrint.val == Status::NoValue)
        return os << "NoValue";
    if (toPrint.val == Status::InActive)
        return os << "InActive";
    throw;
}

int main(void)
{
    Status test(Status::NoValue);
    std::cout << test << std::endl;
    std::cin >> test;
    std::cout << test << std::endl;
}