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C/C++: How to convert int to enum?
Started by , Jul 06
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Is there a way to convert an int to enum?
For example, I declared the following enum type:
wednesday,
Is there a way to set today to Wednesday using an integer, like this:
According to C documents, the following is legal, but result is not defined
today = (Days)0;
&&Members &&-&&Reputation:
Quote:Original post by faculaganymedeAccording to C documents, the following is legal, but result is not definedtoday = (Days)0;My C++ compiler has no problem with that (VS 2003). I've seen casting arbitrary integers to enums like that before, I think that's how you're supposed to do it.EDIT: Is this C or C++? There might be a difference between the two.EDIT2: Yeah, that's the right way in C++ at least. See these links:
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To be safe, define the first element zero.saturday = 0,...Kuphryn
Anonymous Poster_Anonymous Poster_*
&&Guests &&-&&Reputation:
You can do that just fine, without casting.
Another good practice is to have a last enumeration.
For example:enum Days
wednesday,
}DThen you can loop through your enum...for(int i = 0; i & LAST_DAY; i++)
if(today == wednesday)
std::cout && "Today is Hump-Day!!!";
&&Members &&-&&Reputation:
Thanks everyone for your quick feedbacks.I am programming in C++ using MS VS 6.0.Here's MSDN library doc that I was referring to ealier.
The very last line seems to say enum typecast is not possible.---------------------------------------------------------------------------enumenum [tag] {enum-list} [declarator];
// for definition of enumerated type
// for declaration of variable of type tagThe enum keyword specifies an enumerated type.An enumerated type is a user-defined type consisting of a set of named constants called enumerators. By default, the first enumerator has a value of 0, and each successive enumerator is one larger than the value of the previous one, unless you explicitly specify a value for a particular enumerator. Enumerators needn’t have unique values. The name of each enumerator is treated as a constant and must be unique within the scope where the enum is defined. An enumerator can be promoted to an integer value. However, converting an integer to an enumerator requires an explicit cast, and the results are not defined.In C, you can use the enum keyword and the tag to declare variables of the enumerated type. In C++, you can use the tag alone.In C++, enumerators defined within a class are accessible only to member functions of that class unless qualified with the class name (for example, class_name::enumerator). You can use the same syntax for explicit access to the type name (class_name::tag).For related information, see class and struct.Example// Example of the enum keywordenum Days
// Declare enum type Days{
// saturday = 0 by default
sunday = 0,
// sunday = 0 as well
// monday = 1
// tuesday = 2
wednesday,
// Variable today has type Days
// Error, redefinition of tuesdayenum D
// Legal in C and C++D
// Legal in C++ onlyyesterday =int i =
// L i = 2yesterday = 0;
// E no conversionyesterday = (Days)0;
// Legal, but results undefined
&&Members &&-&&Reputation:
Just having done a quick test, in VS.net 2003, this throws up no compiler or runtime errorsenum Days{ Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday,};int _tmain(){ Days normalDay, illegalD normalDay = (Days)2; illegalDay = (Days)234; return 0;}I'm assuming that the documentation is refering to the illegalDay line when describing the casting as undefined.Casting 2 (or any valid number) will give you the corresponding enum.
What 234 gives you I dont know.I really wouldn't worry about this to be honest, as long as you are using valid numbers to cast.
And as long as you have the max days enum mentioned in a earlier post, there should be no chance of you making an error (unless you declare the first value &0, in which case you should be careful)Spree
&&Members &&-&&Reputation:
Keep in mind that your assuming an enum is the size of an int.
It doesn't have to be:).
YOu can force it to be atleast as large as an in by assigning an enum entry to have a value greater than a short or word.An enum can be the size of a char or a int16 or an int 32 or an int64.So casting can be dangerous.CheersCHris
&&Crossbones+ &&-&&Reputation:
As others have mentioned, doing the cast like that should work everywhere as long as the int is legit.
Personally, I've moved away from enums due to other reasons [I tired of doing string-&enum enum-&string conversions...] and only really use them now when the result absolutely never, ever needs displayed or inputed by users or between components. Which is rare to say the least.
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Quote:Original post by kuphrynTo be safe, define the first element zero.saturday = 0,...KuphrynThe value of the first enum element is always 0 if it is not initialized (see the C++ standard, section 7.2, § 1).Regards,
-- Emmanuel D. [] []
&&Members &&-&&Reputation:
Quote:Is there a way to set today to Wednesday using an integer, like this:today = 3According to C documents, the following is legal, but result is not definedtoday = (Days)0;Why not just do this: today =an enumeration is just a list of constants so it would be just the same as doing this:#define saturday
0int today =orconst int saturday = 0;int today =Someone please correct me if i'm wrong.
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Quote:Original post by DigiDude
Why not just do this: today =
For my app, I couldn't do this because I don't know the day beforehand, this data has to be read from a file.
In my original plan, I was suppose to read the data in as a string from the file, e.g. "saturday", but I didn't know how to convert string to enum.
So I thought of using integers to represent days, to make things easier.
today ?= "saturday"
Quote:Original post by Telastyn
Personally, I've moved away from enums due to other reasons [I tired of doing string-&enum enum-&string conversions...] and only really use them now when the result absolutely never, ever needs displayed or inputed by users or between components. Which is rare to say the least.
How do you convert string to enum, and enum to string?
&&Members &&-&&Reputation:
Couldn't you read it in as integers then use a switch statment like:int blah = [whatever you read in from file];Dswitch (blah){case 0:
today =...}
&&Crossbones+ &&-&&Reputation:
Quote:Original post by faculaganymedeHow do you convert string to enum, and enum to string?Something like this:enum hextypes
{NOTHING,GRASSLAND,PLAINS,SPARCEFOREST,FOREST,SWAMP,HILL,MOUNTAIN,DESERT,TUNDRA,JUNGLE,SHALLOWS,OCEAN,HEXTYPECOUNT};
char *hextypesymbols[]
={"_","g","p","f","F","w","h","M","d","t","j","-","~"};char *hextypenames[]={"nothing","grassland","plains","sparceforest","forest","swamp","hill","mountain","desert","tundra","jungle","shallows","ocean"};intchar
ht=NOTHING;cout && hextypenames[FOREST];for (x=0;x&HEXTYPECOUNT;++x){
if (buf==strstr(buf,hextypenames[x])){
ht=(hextypes)x;
}}though using char * is asking for trouble. And editing a source file whenever you want to add a new enum is asking for trouble. And keeping 2-3 arrays in perfect sync is asking for trouble.So I don't do this any more. I made a templated class which stores a name/ID pair as well as arbitrary properties associated with them. It then can convert nicely between the std::string, the ID, and the properties. Like for the example above, the properties like how much food a hextype yields when farmed is now stored along with the name/ID, rather than a seperate table using the enum as a key. The bonus is that the ID's can be dynamically generated, so the name/ID/properties can be loaded from file or otherwise generated at run-time.Benefits all around.
&&Members &&-&&Reputation:
To be totally safe just don't make today type Days (plural type names feel so wrong), use a normal number typeenum Days
// Declare enum type Days{
// saturday = 0 by default
// sunday = 1
// monday = 2
// tuesday = 3
wednesday,
friday}You can still use the enum constants outside the type & they function exactly as their number counterpartsI often use unnamed enums just for storing constant values, the downside though is that enums can only be intergral(also unnamed types aren'])
_______________________________ ________ _____ ___ __ _`By offloading cognitive load to the computer, programmers are able to design more elegant systems' - Unununium OS regarding Python
&&Members &&-&&Reputation:
Quote:Original post by DigiDudeCouldn't you read it in as integers then use a switch statment like:int blah = [whatever you read in from file];Dswitch (blah){case 0:
today =...}Why would you want to replace what could be a single line of code with a huge switch statement?
Progress is born from the opportunity to make mistakes.My prize winning
looks one move ahead, can you beat it?
&&Members &&-&&Reputation:
Quote:Original post by DigiDudeCouldn't you read it in as integers then use a switch statment like:Thanks.
Enum Days is just a quick and dirty example.
In the actual app, the list may be very long, so using a switch statement requires a long list of cases.
But, it's definitely an idea worth considering.Quote:Original post by Telastynthough using char * is asking for trouble. And editing a source file whenever you want to add a new enum is asking for trouble. And keeping 2-3 arrays in perfect sync is asking for trouble.Yes, I agree.
This is very messy.
Thanks for sharing :)
Anonymous Poster_Anonymous Poster_*
&&Guests &&-&&Reputation:
Quote:Original post by faculaganymedeHi all,Is there a way to convert an int to enum?For example, I declared the following enum type:*** Source Snippet Removed ***Is there a way to set today to Wednesday using an integer, like this:today = 3This is legal in C so long as one of the enumerated constants has the value 3.Quote:According to C documents, the following is legal, but result is not definedtoday = (Days)0;This is legal in C so long as one of the enumerated constants has the value 0.C++ may require a cast, I'm not sure.
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