how to use enum when reading from a file

Question

i'm a begginer in c++ and I need to make some automobile related classes that need to be read from a file.In one of them I want to use an enum my class looks like this:

enum engines{ gasoline, hybrid, diesel };

class Automobil
    {
    const int id;
    char *model;
    engines engine;
    int max_speed;
    int engine_cc;
    float avg_consumption_urban;
    float avg_consumption;
    float avg_speed_urban;
    float avg_speed;
}

and i need to overload the >> operator to read the object from a file but when I do it for the engine,I have errors. How do I still keep the enum and read from the file?

friend ifstream& operator>>(ifstream& input, Automobil &a)
{
    delete[] a.model;
    input >> a.model;
    input >>a.engine; //error here
    input >> a.max_speed;
    input >> a.engine_cc;
    input >> a.avg_consumption_urban;
    input >> a.avg_speed_urban;
    input >> a.avg_consumption;
    input >> a.avg_speed;
    return input;

}

I recommend searching the internet for examples. I recently saw a similar question posted. — Thomas Matthews, Dec 21 '15 at 20:49
i copied it all from the other overload that's not necessary.. I don't quite know what to search anymore because I didn't find examples related to my question.. — Ramona Mihaela Dinescu, Dec 21 '15 at 20:51
I used "stackoverflow c++ read enum" and came across this question: [Reading in from a .txt file to a struct array that contains enum](http://stackoverflow.com/questions/28531933/reading-in-from-a-txt-file-to-a-struct-array-that-contains-enum). Looks like I answered it too. :-) — Thomas Matthews, Dec 21 '15 at 20:58
BTW, remove `delete [] a.model;` because you will be reading into memory that has been deleted and it could be reused by other functions. — Thomas Matthews, Dec 21 '15 at 21:06

Thomas Matthews · Accepted Answer · 2015-12-21T21:04:37.647

There is no overloaded form of operator>> to read in enumerations.

You have two choices:

Read in enumeration name and convert to the enum class.
Read in enumeration value (number) and convert to enum class.

I prefer using the name method. Read in the name as a string, and look up in a table of [name, enum], to convert it.

Edit 1: An implementation

std::map<std::string, enum engines> conversion_table;
// Initialization
conversion_table["gasoline"] = engines::gasoline;
conversion_table["hybrid"]   = engines::hybrid;
conversion_table["electric"] = engines::electric;

Note: you may have to remove engines:: from the values.

To convert text to enum:

engines engine_type = conversion_table[text];

how to use enum when reading from a file

1 Answers1