Assigning enum value to integer crashes program [closed] - c++

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I have created an enum with these values:
enum Car_Manufacturer
{
AUDI = 1,
CHRYSLER = 2,
FORD = 3,
HONDA = 4,
LEXUS = 5,
NISSAN = 6,
MERCEDES = 7,
PORSCHE = 8,
VOLVO = 9
};
I have the user enter a character which corresponds to the model of car they want to view. I need the character the user entered to become a integer which corresponds to the values in the enum so that I can easily search through an array to find a car of the correct make. The function I created looks like this:
int set_car_make_ch( char input )
{
int manufacturer = 0;
if( input == 'A' )
{
manufacturer = AUDI;
}
else if( input == 'C' )
{
manufacturer = CHRYSLER;
}
else if( input == 'F' )
{
manufacturer = (int)FORD;
}
else if( input == 'H' )
{
manufacturer = HONDA;
}
else if( input == 'L' )
{
manufacturer = LEXUS;
}
else if( input == 'M' )
{
manufacturer = MERCEDES;
}
else if( input == 'N' )
{
manufacturer = NISSAN;
}
else if( input == 'P' )
{
manufacturer = PORSCHE;
}
else if( input == 'V' )
{
manufacturer = VOLVO;
}
else
{
cout<<"Invalid Car Manufacturer, please edit the input file."<<endl;
exit( EXIT_FAILURE );
}
return manufacturer;
}
The program freezes and crashes when an enum value attempts to be assigned to an integer. I am using the G++ compiler. Any help with this issue would be greatly appreciated.

Answer 1

Please, use a lookup table or a switch statement rather than the if-else-if ladder.
Lookup Table
struct Car_Text_Enum_Entry
{
const char * name;
Car_Manufacturer enum_value;
};
const static Car_Text_Enum_Entry enum_conversion[] =
{
{"AUDI", AUDI},
{"BMW", BMW},
{"DODGE", DODGE},
//...
};
const unsigned int number_of_conversions =
sizeof(enum_conversion) / sizeof(enum_conversion[0]);
Car_Manufacturer Car_Text_To_Enum(char car_mfg_letter)
{
Car_Manufacturer manufacturer = 0;
for (unsigned int i = 0; i < number_of_conversions; ++i)
{
if (enum_conversion[i].name[0] == car_mfg_letter)
{
manufacturer = enum_conversion[i].enum_value;
break;
}
}
return manufacturer;
}
The lookup table is a lot tighter code and to added or remove manufacturers only requires changing the table, not the code.
Switch Statement
The switch statement approach will work for letters, but not for strings. For strings, use a lookup table.
Car_Manufacturer Car_Mfg_Letter_To_Enum(char car_mfg_letter)
{
Car_Manufacturer manufacturer;
switch (car_mfg_letter)
{
case 'A' : manufacturer = AUDI; break;
case 'B' : manufacturer = BMW; break;
case 'D' : manufacturer = DODGE; break;
case 'H' : manufacturer = HONDA; break;
// ...
}
return manufacturer;
}
The switch statement approach is still more readable and easier to maintain than the if-else-if ladder. However, it will not work with strings (a.k.a. multiple letters).
Maps
However, if you have learned about std::map, you can use it also:
typedef std::map<char, Car_Manufacturer> Car_Mfg_Container;
Car_Mfg_Container car_mfg_association;
// Initialization:
car_mfg_association['A'] = AUDI;
car_mfg_association['B'] = BMW;
//...
Car_Manufacturer Car_Mfg_Letter_To_Enum(char car_mfg_letter)
{
return car_mfg_association[car_mfg_letter];
}
Unlike the static, constant, lookup table, the std::map must be initialized during runtime.
So, please, don't use if-else-if ladders for things that can be looked up in a table.
Also, with enumerations, you only need to assign a value to the first item.

Answer 2

You have not explained what (if any...) error message you are getting or how you are using this function, but it's generally not a good idea to rely implicit or C style casting from enum to int when you have better tools available in C++:
Try this: Declare your variable as type Car_Manufacturer:
Car_Manufacturer manufacturer{};
If for some reason you must use int try this:
manufacturer = static_cast < int >(FORD);
If there is something else wrong, instead of just crashing because you're doing an explicit, C style cast, you should get a reasonable error message from static_cast.
The best way to avoid such issues entirely is to use C11's Scoped enumerations, which are strongly typed and cannot simply be cast as integers.
(As an aside, as #ThomasMatthews has explained, use switch, not if/else if when you have an enum, char or int.)