Thread: loop control in macro?

Hi, Gurus,

Pure C, I am trying to define a enum type with variable number of elements, controlled by macro.

for example

Code:

#define A 2

typdef enum
{
A_0
A_1
} ENUM_TABLE

is there a way to make this enum definition automatic populate bases on definition of "A"
A_0, ...A_#(A-1),

Great, thanks,

By "pure" C, I assume you mean standard and portable, and I'm not aware of any way to do that. There is the __COUNTER__ preprocessing symbol but I don't think it's standard, and I don't know how you would stop it at A-1. I'm also not sure why you would want to something like that. The way I see it, if you have items for which a simple number is all you need to distinguish them, then I would use an array, where the name of the array reflects it's use/purpose (A in your example), and the index corresponds to the number in your example, and you just define A_MAX for the size of the array. If the values are distinguished by something more significant than a number, then it seems like appending a word would be best, such as A_FOO, A_BAR, which can't really be automated anyhow.

Maybe if you could explain in more detail what specifically you're trying to do we could help you find a solution.

Great thanks to all prompt comments,

I am trying to do something like this: a enum type has "A" elements, naming of the elements doesn't really matter, reason to choose "A_#" is for possible loop control.

number of elements in the enum type should be variable.
One case:

Code:

#define A 100

Another case:

Code:

#define A 1000

If it's doable, I can have a code smart enough at precompile to generate variable size of the ENUM.

I don't imaging variable switch case is possible. So didn't ask,

Originally Posted by legendbb

I am trying to do something like this: a enum type has "A" elements, naming of the elements doesn't really matter, reason to choose "A_#" is for possible loop control.

There's no 'eval' function in C. You can't take some loop control variable, like i, and have it's value be turned into a symbol during run-time. You can only append the symbol name (i) to A, so every iteration of your loop will produce A_i regardless of i's value. You can never get A_3, A_42, etc. I think you're heading down the wrong path. Seriously, this sounds like a great case for using arrays.

Boost's preprocessor library can do it. AFAIK it's solely implemented using the preprocessor which I don't think has changed significantly between C and C++. Of course, just because it (might) be possible doesn't mean it's a good idea.

Great thanks to all comment, I give up this idea.