🚀 go-pugleaf

mtm4@rsvl.unisys.com (Michael McCormick) writes:

>"W. Dicks" <wd@isis.co.za> shared the following on 13 Mar 96 07:31:13 GMT:

>>The system that I'm working often needs to know the string 
>>value of an enum. e.g. enum week{MON=1, ..., SUN} it; it = 
>>TUE;
>>Then when this enum is passed as a parameter the function 
>>should return the string based on the enum. For instance, 
>>weekImage(it) will return "TUE". Is it not possible that such 
>>a functionality can be built into enums?

>What you are essentially asking for is language support for converting
>a label into a string respresentation of its name.  That is a very
>unusual feature to find in any language, since it would require the
>compiler to place the symbolic dictionary in the executable file.

It would not in fact be difficult to do, since only a table of
strings per enum type would be needed. The information is normally
put into debug info if you compile in debug mode anyway so the
debugger can display the labels instead of the values. A language
mechanism to make that data always available is probably too
expensive a price for every program to pay in order to support
this requirement which isn't very common and which can be solved
easily in source code.


>Since enum is by definition an integral type, why not assign values to your
>enumerators that can be used as indexes into a string?:

> enum week {MON=0,TUE=4,WED=8,THU=12,FRI=16,SAT=20,SUN=24};
> const char * days = "MON\0TUE\0WED\0THU\0FRI\0SAT\0SUN";

> char const * weekImage(week day) = days[day];

I would suggest instead this approach, which does not require you
to count characters:
const char* days[] = {"MON", "TUE", "WED", "THU", "FRI", "SAT", "SUN"};
It "wastes" 7 extra pointers, but is easier to write and maintain.

The more general case of non-contiguous enum values could be handled
by a table of value/string pairs and a lookup function. The standard
"map" class will do it all for you.
--
Steve Clamage, stephen.clamage@eng.sun.com
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