How to assign a value to an enum based on input from a file in C++?

Question

I have a file with values like: START and STOP. I also have the following enum declared:

enum Type {
    START,
    STOP
};

I'm trying to set the enum equal to the first value in the file with something like this:

enum Type foo;

ifstream ifile;
ifile.open("input.txt");

ifile >> foo;

I'm getting the error: no match for ‘operator>>’ in ‘ifile >> foo’.

How do I go about doing this correctly?

Answer 1

The quickest thing to do is to read in an int and cast it to your Type enum.

Answer 2

@popester

I'd post this as a response but from past experience code doesn't translate too well in post replies on SO.

I just wrote up the following short program to test what you suggested:

#include <iostream>
#include <fstream>

using namespace std;

int main() {
    enum Type {
        START,
        STOP
    };

    int bar;
    enum Type foo;

    ifstream ifile;
    ifile.open("input.txt");

    ifile >> bar;

    foo = (Type) bar;
    cout << "bar: " << bar << endl;

    cout << "foo: " << foo << endl;
}

Below is my input.txt file:

STOP

I compiled and ran the program and it output the following:

bar: -1207974988
foo: -1207974988

Am I just misunderstanding what you're suggesting? If you could lead me in the right direction that would be great. Thanks for your help.

Answer 3

The stream insertion operator is not overloaded for user defined types. You can either define one for your enum object of type Type or use one of the existing overloads for reading unsigned char or bool and then change the value to your enum.

Answer 4

http://condensedcpp.com/Enums.html

std::istream& operator >> (std::istream& i, Season& season)
{
    season = SPRING;
    std::string value;
    if (i >> value) {
        if (value == "Summer") {
            season = SUMMER;
        }
        else if (value == "Autumn") {
            season = AUTUMN;
        }
       else if (value == "Winter") {
            season = WINTER;
        }
    }
    return i;
}

Answer 5

I've found for my particular situation that the following code is the best solution:

template <class T> T a2e(string c, const string a[], const int size) {
    for (int i=0; i < size; i++) {
        if (c == a[i]) {
            return static_cast<T>(i);
        }
    }
}

And would be used as follows:

enum StateType {START, STOP};
const int MAXVALUES = STOP+1;
const string stateNames[MAXVALUES] = {"START", "STOP"};

enum StateType state;

ifstream ifile;
ifile.open("input.txt");

ifile >> foo;
state = a2e <enum StateType> (foo, stateNames, MAXVALUES);

Hope this helps someone in the future. Thanks to everyone who made suggestions about how to tackle this problem.