enum question

[James Brown]

I have the following enum declared:

enum TOKEN { TOK_ID = 1000, TOK_NUMBER, TOK_STRING };

(it goes on and on like that)

This is what I would like to do:

TOKEN t1 = TOK_ID; // ok
TOKEN t2 = 5; // compile error (cannot convert from
const int to 'enum TOKEN')
TOKEN t3 = (TOKEN)5; // compiles but I think it's illegal???

could someone clarify if the 3rd example is ok or not, and what type
of problem I might expect if it isn't ok?

What I am trying to do is represent ASCII values 0-127 as TOKENs (this is
why I
started the TOKEN enum off at '1000' so I had plenty of space at the
start....and I don't
really want to type out 127 values into my enum declaration....can anybody
suggest
an alternate solution?

thanks,
James

 

[Chad]

I have the following enum declared:

enum TOKEN { TOK_ID = 1000, TOK_NUMBER, TOK_STRING };

(it goes on and on like that)

This is what I would like to do:

TOKEN t1 = TOK_ID; // ok
TOKEN t2 = 5; // compile error (cannot convert from
const int to 'enum TOKEN')
TOKEN t3 = (TOKEN)5; // compiles but I think it's illegal???

could someone clarify if the 3rd example is ok or not, and what type
of problem I might expect if it isn't ok?

What I am trying to do is represent ASCII values 0-127 as TOKENs (this is
why I
started the TOKEN enum off at '1000' so I had plenty of space at the
start....and I don't
really want to type out 127 values into my enum declaration....can anybody
suggest
an alternate solution?

thanks,
James

In the expression:

enum TOKEN { TOK_ID = 1000, TOK_NUMBER, TOK_STRING };

TOK_ID, TOK_NUMBER, and TOK_STRING are constant integer values. In this
case, TOK_ID is = 1000, then TOK_NUMBER is 1001. The reason why the
compiler is b-tching is because you are trying to modify the constant
integer TOK_NUMBER (which has a value of 1001).

 

[Keith Thompson]

I have the following enum declared:

enum TOKEN { TOK_ID = 1000, TOK_NUMBER, TOK_STRING };

(it goes on and on like that)

This is what I would like to do:

TOKEN t1 = TOK_ID; // ok
TOKEN t2 = 5; // compile error (cannot convert from
const int to 'enum TOKEN')
TOKEN t3 = (TOKEN)5; // compiles but I think it's illegal???

could someone clarify if the 3rd example is ok or not, and what type
of problem I might expect if it isn't ok?

The declaration "enum TOKEN { ... };" creates a type called
"enum TOKEN". It does not create a type called TOKEN.

Given the type declaration, the declaration
enum TOKEN t2 = 5;
is perfectly legal.

I suspect you're using a C++ compiler. C++ is a different language
with different rules; comp.lang.c++ is down the hall on the left.

 

[Keith Thompson]

In the expression:

enum TOKEN { TOK_ID = 1000, TOK_NUMBER, TOK_STRING };

That's a declaration, not an expression.

TOK_ID, TOK_NUMBER, and TOK_STRING are constant integer values. In this
case, TOK_ID is = 1000, then TOK_NUMBER is 1001.
Yes.

The reason why the
compiler is b-tching is because you are trying to modify the constant
integer TOK_NUMBER (which has a value of 1001).

Look again. There's nothing in the original poster's code that
attempts to modify TOK_NUMBER.

 

[Chad]

The declaration "enum TOKEN { ... };" creates a type called
"enum TOKEN". It does not create a type called TOKEN.

Given the type declaration, the declaration
enum TOKEN t2 = 5;
is perfectly legal.

I suspect you're using a C++ compiler. C++ is a different language
with different rules; comp.lang.c++ is down the hall on the left.

I'm calling an offsides on this one. Maybe I mis-understood the
question. I always thought when you has a construction like

enum TOKEN { TOK_ID = 1000, TOK_NUMBER, TOK_STRING };

Then TOK_NUMBER = 1001 and TOK_STRING = 1002. Both of these being
constant integers (Page 39 of the "C Programming Language" by K & R).
Hence these values could not be modified because they are constant.

 

[Michael Mair]

I'm calling an offsides on this one. Maybe I mis-understood the
question. I always thought when you has a construction like

enum TOKEN { TOK_ID = 1000, TOK_NUMBER, TOK_STRING };

Then TOK_NUMBER = 1001 and TOK_STRING = 1002. Both of these being
constant integers (Page 39 of the "C Programming Language" by K & R).
Hence these values could not be modified because they are constant.

I am not sure what you mean.
The
enum TOKEN {
....
};
declaration gives us the type "enum TOKEN", quite like
struct foo {
....
};
gives us the type "struct foo".

So,
enum TOKEN t2;
t2 = 5;
or
enum TOKEN t2 = 5;
are structurally not different from
struct foo bar;
bar = baz;
or
struct foo bar = baz;
where baz is of type struct foo.

Declaring t2 certainly does not change any of the enumeration
constants, neither does initializing t2.


Cheers
Michael

 

[James Brown]

The declaration "enum TOKEN { ... };" creates a type called
"enum TOKEN". It does not create a type called TOKEN.

Given the type declaration, the declaration
enum TOKEN t2 = 5;
is perfectly legal.

I suspect you're using a C++ compiler. C++ is a different language
with different rules; comp.lang.c++ is down the hall on the left.

--
Keith Thompson (The_Other_Keith) (e-mail address removed)
<http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*>
<http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

Hi,
thanks for your answer - and you're right, I am using C++ but its useful for
me
to appreciate the differences....I'll repost on c.l.c++

thanks,
James

 

[Keith Thompson]

The declaration "enum TOKEN { ... };" creates a type called
"enum TOKEN". It does not create a type called TOKEN.

Given the type declaration, the declaration
enum TOKEN t2 = 5;
is perfectly legal.

I suspect you're using a C++ compiler. C++ is a different language
with different rules; comp.lang.c++ is down the hall on the left.

[...]
I'm calling an offsides on this one. Maybe I mis-understood the
question. I always thought when you has a construction like

enum TOKEN { TOK_ID = 1000, TOK_NUMBER, TOK_STRING };

Then TOK_NUMBER = 1001 and TOK_STRING = 1002. Both of these being
constant integers (Page 39 of the "C Programming Language" by K & R).
Hence these values could not be modified because they are constant.

Of course you can't modify TOK_NUMBER or TOK_STRING.

The posted code (see above) doesn't attempt to do so, and I don't see
anything that would lead you to believe that it does.

 

[Emmanuel Delahaye]

James Brown a écrit :

enum TOKEN { TOK_ID = 1000, TOK_NUMBER, TOK_STRING };

TOKEN t1 = TOK_ID; // ok
TOKEN t2 = 5; // compile error (cannot convert from
const int to 'enum TOKEN')

Be sure you are using a C compiler. The C-language is not that strongly
typed. This line is fine C.

TOKEN t3 = (TOKEN)5; // compiles but I think it's illegal???

It's fine C too.

 

[Eric Sosman]

James Brown a écrit :



Be sure you are using a C compiler. The C-language is not that strongly
typed. This line is fine C.



It's fine C too.

Ah. This is obviously some strange usage of the word
"fine" that I wasn't previously aware of.

enum TOKEN { TOK_ID = 1000, TOK_NUMBER, TOK_STRING };
TOKEN t1 = TOK_ID;
TOKEN t2 = 5;
TOKEN t3 = (TOKEN)5;

gcc -W -Wall -ansi -pedantic -c token.c
token.c:2: error: parse error before "t1"
token.c:2: warning: type defaults to `int' in declaration of `t1'
token.c:2: error: ISO C forbids data definition with no type or storage
class
token.c:3: error: parse error before "t2"
token.c:3: warning: type defaults to `int' in declaration of `t2'
token.c:3: error: ISO C forbids data definition with no type or storage
class
token.c:4: error: parse error before "t3"
token.c:4: warning: type defaults to `int' in declaration of `t3'
token.c:4: error: `TOKEN' undeclared here (not in a function)
token.c:4: error: parse error before numeric constant

 

[Emmanuel Delahaye]

Eric Sosman a écrit :

Ah. This is obviously some strange usage of the word
"fine" that I wasn't previously aware of.

Ah sh*t, I missed the 'enum' word... Sorry about that.