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C/C++: How to convert int to enum?

load_bitmap_file · 2005-07-06T15:09:56

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:OneTwo

General and Gameplay Programming Programming

Started by faculaganymede July 06, 2005 03:06 PM

15 comments, last by GameDev.net 18 years, 10 months ago

faculaganymede

145

Author

July 06, 2005 04:33 PM

Quote:Original post by DigiDude
Why not just do this:
today = saturday;

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 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.<!–QUOTE–></td></tr></table></BLOCKQUOTE><!–/QUOTE–><!–ENDQUOTE–><br>How do you convert string to enum, and enum to string?

KittyRa

262

July 06, 2005 04:43 PM

Couldn't you read it in as integers then use a switch statment like:

int blah = [whatever you read in from file];Days today;switch (blah){case 0:    today = saturday;    break;...}

F-R-E-D F-R-E-D-B-U-R...G-E-R! - Yes!

Telastyn

3,778

July 06, 2005 04:44 PM

Quote:Original post by faculaganymede

How 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};       // more later...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"};/* snip *//* example */int      x;char     *buf;hextype  ht=NOTHING;// assign buf somehowcout << 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.

-- Tangent Developer Journal - Delegates - Part 2

ProPuke

466

July 06, 2005 04:47 PM

To be totally safe just don't make today type Days (plural type names feel so wrong), use a normal number type

enum Days               // Declare enum type Days{   saturday,            // saturday = 0 by default   sunday,          	// sunday = 1   monday,              // monday = 2   tuesday,             // tuesday = 3   wednesday,           // etc.   thursday,   friday}int today;

You can still use the enum constants outside the type & they function exactly as their number counterparts
I often use unnamed enums just for storing constant values, the downside though is that enums can only be intergral
(also unnamed types aren't standard ;])

_______________________________ ________ _____ ___ __ _`By offloading cognitive load to the computer, programmers are able to design more elegant systems' - Unununium OS regarding Python

InsaneBoarder234

174

July 06, 2005 04:57 PM

Quote:Original post by DigiDude
Couldn't you read it in as integers then use a switch statment like:
int blah = [whatever you read in from file];Days today;switch (blah){case 0:    today = saturday;    break;...}

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 Connect 4 AI looks one move ahead, can you beat it? @nickstadb

faculaganymede

145

Author

July 06, 2005 05:09 PM

Quote:Original post by DigiDude
Couldn'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 Telastyn
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.

Yes, I agree. This is very messy. Thanks for sharing :)

Anonymous

July 06, 2005 08:53 PM

Quote:Original post by faculaganymede
Hi 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 = 3

This 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 defined
today = (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.

C/C++: How to convert int to enum?

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